Associative array/Merging

Task

Define two associative arrays, where one represents the following "base" data:


Key	Value
"name"	"Rocket Skates"
"price"	12.75
"color"	"yellow"

And the other represents "update" data:


Key	Value
"price"	15.25
"color"	"red"
"year"	1974

Merge these into a new associative array that contains every key found in either of the source ones. Each key should map to the value in the second (update) table if that exists, or else to the value in the first (base) table. If possible, do this in a way that does not mutate the original two associative arrays. Obviously this should be done in a way that would work for any data, not just the specific data given here, but in this example the result should be:


Key	Value
"name"	"Rocket Skates"
"price"	15.25
"color"	"red"
"year"	1974

11l

Translation of: Python

V base = [‘name’ = ‘Rocket Skates’, ‘price’ = ‘12.75’, ‘color’ = ‘yellow’]
V update = [‘price’ = ‘15.25’, ‘color’ = ‘red’, ‘year’ = ‘1974’]

V result = copy(base)
result.update(update)

print(result)

Output:

[color = red, name = Rocket Skates, price = 15.25, year = 1974]

Ada

with Ada.Text_Io;
with Ada.Containers.Indefinite_Ordered_Maps;

procedure Merge_Maps is
   use Ada.Text_Io;

   type Key_Type   is new String;
   type Value_Type is new String;

   package Maps is
     new Ada.Containers.Indefinite_Ordered_Maps (Key_Type     => Key_Type,
                                                 Element_Type => Value_Type);
   use Maps;

   function Merge (Original : Map; Update : Map) return Map is
      Result : Map    := Original;
      Cur    : Cursor := Update.First;
   begin
      while Has_Element (Cur) loop
         if Original.Contains (Key (Cur)) then
            Result.Replace_Element (Result.Find (Key (Cur)),
                                    Element (Cur));
         else
            Result.Insert (Key (Cur), Element (Cur));
         end if;
         Next (Cur);
      end loop;
      return Result;
   end Merge;

   procedure Put_Map (M : Map) is
      Cur : Cursor := M.First;
   begin
      while Has_Element (Cur) loop
         Put (String (Key (Cur)));
         Set_Col (12);
         Put (String (Element (Cur)));
         New_Line;
         Next (Cur);
      end loop;
   end Put_Map;

   Original : Map;
   Update   : Map;
   Result   : Map;
begin
   Original.Insert ("name", "Rocket Skates");
   Original.Insert ("price", "12.75");
   Original.Insert ("color", "yellow");

   Update.Insert ("price", "15.25");
   Update.Insert ("color", "red");
   Update.Insert ("year", "1974");

   Result := Merge (Original, Update);

   Put_Line ("Original:");
   Put_Map (Original);
   New_Line;

   Put_Line ("Update:");
   Put_Map (Update);
   New_Line;

   Put_Line ("Result of merge:");
   Put_Map (Result);
   New_Line;

end Merge_Maps;

Output:

Original:
color      yellow
name       Rocket Skates
price      12.75

Update:
color      red
price      15.25
year       1974

Result of merge:
color      red
name       Rocket Skates
price      15.25
year       1974

ALGOL 68

Works with: ALGOL 68G version Any - tested with release 2.8.3.win32

Uses the associative array implementations in ALGOL_68/prelude.

# associative array merging                                                  #
 
# the modes allowed as associative array element values - change to suit     #
MODE AAVALUE = UNION( STRING, INT, REAL );
# the modes allowed as associative array element keys - change to suit       #
MODE AAKEY   = STRING;
# initial value for an array element                                         #
AAVALUE init element value = "";
 
# include the associative array code                                         #
PR read "aArrayBase.a68" PR
 
# adds or replaces all elements from b into a                     #
PRIO UPDATE = 9;
OP UPDATE = ( REF AARRAY a, REF AARRAY b )REF AARRAY:
BEGIN
    REF AAELEMENT e := FIRST b;
    WHILE e ISNT nil element DO
        a // key OF e := value OF e;
        e := NEXT b
    OD;
    a
END # UPDATE # ;

BEGIN # tests                                                     #
    # construct the associative arrays for the task               #
    REF AARRAY a := INIT LOC AARRAY;
    REF AARRAY b := INIT LOC AARRAY;
    a // "name"  := "Rocket Skates";
    a // "price" := 12.75;
    a // "color" := "yellow";
    b // "price" := 15.25;
    b // "color" := "red";
    b // "year"  := 1974;
    # merge the arrays                                            #
    REF AARRAY c := INIT LOC AARRAY;
    c UPDATE a UPDATE b;
    # show the merged array                                       #
    REF AAELEMENT e := FIRST c;
    WHILE e ISNT nil element DO
        print( ( key OF e
               , ": "
               , CASE value OF e
                   IN (STRING s): s
                    , (INT    i): whole( i, 0 )
                    , (REAL   r): fixed( r, -12, 2 )
                  OUT "????"
                 ESAC
               , newline
               )
             );
        e := NEXT c
    OD
END

Output:

name: Rocket Skates
year: 1974
price:        15.25
color: red

AppleScript

The method with AppleScript "records" is to concatenate them. The result is a third record containing the labels from both contributors, the values from the record to the left of the operator being kept where labels are shared. The bars with some of the labels below are to distinguish them as "user" labels from tokenised ones that are provided as standards for use by scriptable applications and scripting additions. However, merging records works with tokenised labels too.

set baseRecord to {|name|:"Rocket Skates", price:12.75, |color|:"yellow"}
set updateRecord to {price:15.25, |color|:"red", |year|:1974}

set mergedRecord to updateRecord & baseRecord
return mergedRecord

Output:

{price:15.25, |color|:"red", |year|:1974, |name|:"Rocket Skates"}

Arturo

details: #[name: "Rocket Skates" price: 12.75 colour: 'yellow]
newDetails: extend details #[price: 15.25 colour: 'red year: 1974]

print newDetails

Output:

[name:Rocket Skates price:15.25 colour:red year:1974]

AutoHotkey

merge(base, update){
	Merged  := {}
	for k, v in base
		Merged[k] := v
	for k, v in update
		Merged[k] := v
	return Merged
}

Examples:

base := {"name":"Rocket Skates", "price":12.75, "color":"yellow"}
update := {"price":15.25, "color":"red", "year":1974}
Merged := merge(base, update)
for k, v in Merged
	result .= k " : " v "`n"
MsgBox % result

Outputs:

color : red
name : Rocket Skates
price : 15.25
year : 1974

AWK

# syntax: GAWK -f ASSOCIATIVE_ARRAY_MERGING.AWK
#
# sorting:
#   PROCINFO["sorted_in"] is used by GAWK
#   SORTTYPE is used by Thompson Automation's TAWK
#
BEGIN {
    PROCINFO["sorted_in"] = "@ind_str_asc" ; SORTTYPE = 1
    arr1["name"] = "Rocket Skates"
    arr1["price"] = "12.75"
    arr1["color"] = "yellow"
    show_array(arr1,"base")
    arr2["price"] = "15.25"
    arr2["color"] = "red"
    arr2["year"] = "1974"
    show_array(arr2,"update")
    for (i in arr1) { arr3[i] = arr1[i] }
    for (i in arr2) { arr3[i] = arr2[i] }
    show_array(arr3,"merged")
    exit(0)
}
function show_array(arr,desc,  i) {
    printf("\n%s array\n",desc)
    for (i in arr) {
      printf("%-5s : %s\n",i,arr[i])
    }
}

Output:

base array
color : yellow
name  : Rocket Skates
price : 12.75

update array
color : red
price : 15.25
year  : 1974

merged array
color : red
name  : Rocket Skates
price : 15.25
year  : 1974

B4X

Dim m1 As Map = CreateMap("name": "Rocket Skates", "price": 12.75, "color": "yellow")
Dim m2 As Map = CreateMap("price": 15.25, "color": "red", "year": 1974)
Dim merged As Map
merged.Initialize
For Each m As Map In Array(m1, m2)
	For Each key As Object In m.Keys
		merged.Put(key, m.Get(key))
	Next
Next
Log(merged)

BASIC

BaCon

DECLARE base$, update$, merge$ ASSOC STRING

base$("name") = "Rocket Skates"
base$("price") = "12.75"
base$("color") = "yellow"

PRINT "Base array"
FOR x$ IN OBTAIN$(base$)
    PRINT x$, " : ", base$(x$)
NEXT

update$("price") = "15.25"
update$("color") = "red"
update$("year") = "1974"

PRINT NL$, "Update array"
FOR x$ IN OBTAIN$(update$)
    PRINT x$, " : ", update$(x$)
NEXT

merge$() = base$()
merge$() = update$()

PRINT NL$, "Merged array"
FOR x$ IN OBTAIN$(merge$)
    PRINT x$, " : ", merge$(x$)
NEXT

Output:

Base array
name : Rocket Skates
color : yellow
price : 12.75

Update array
year : 1974
color : red
price : 15.25

Merged array
name : Rocket Skates
year : 1974
color : red
price : 15.25

BASIC256

Translation of: FreeBASIC

dim original(3, 2)
original[0, 0] = "name": original[0, 1] = "Rocket Skates"
original[1, 0] = "price": original[1, 1] = "12.75"
original[2, 0] = "color": original[2, 1] = "yellow"

dim update(3, 2)
update[0, 0] = "price": update[0, 1] = "15.25"
update[1, 0] = "color": update[1, 1] = "red"
update[2, 0] = "year": update[2, 1] = "1974"

dim merged(6, 2)

for i = 0 to 2
	merged[i, 0] = update[i, 0]
	merged[i, 1] = update[i, 1]
next i

index = 3
for i = 0 to 2
	found = False
	for j = 0 to 2
		if original[i, 0] = update[j, 0] then
			found = True
			exit for
		end if
	next j
	if not found then
		merged[index, 0] = original[i, 0]
		merged[index, 1] = original[i, 1]
		index += 1
	end if
next i

for i = 0 to index - 1
	print "key: "; merged[i, 0]; ", value: "; merged[i, 1]
next i

Output:

Same as FreeBASIC entry.

Chipmunk Basic

Works with: Chipmunk Basic version 3.6.4

100 cls
110 dim original$(3,2)
120 original$(0,0) = "name"
130 original$(0,1) = "Rocket Skates"
140 original$(1,0) = "price"
150 original$(1,1) = "12.75"
160 original$(2,0) = "color"
170 original$(2,1) = "yellow"
180 dim update$(3,2)
190 update$(0,0) = "price"
200 update$(0,1) = "15.25"
210 update$(1,0) = "color"
220 update$(1,1) = "red"
230 update$(2,0) = "year"
240 update$(2,1) = "1974"
250 dim merged$(6,2)
270 for i = 0 to 2
280   merged$(i,0) = update$(i,0)
290   merged$(i,1) = update$(i,1)
300 next i
320 index = 3
330 for i = 0 to 2
340   found = 0
350   for j = 0 to 2
360     if original$(i,0) = update$(j,0) then
370       found = 1
380       goto 400
390     endif
400   next j
410   if found = 0 then
420     merged$(index,0) = original$(i,0)
430     merged$(index,1) = original$(i,1)
440     index = index+1
450   endif
460 next i
480 for i = 0 to index-1
490   print "key: ";merged$(i,0);", value: ";merged$(i,1)
500 next i
510 end

Output:

Same as FreeBASIC entry.

FreeBASIC

Type Dictionary
    As String key
    As String value
End Type

Sub merge(original() As Dictionary, update() As Dictionary, result() As Dictionary)
    Dim As Integer i, j, index
    Dim As Boolean found
    
    For i = 0 To Ubound(update)
        result(i) = update(i)
    Next i
    
    index = i
    For i = 0 To Ubound(original)
        found = False
        For j = 0 To Ubound(update)
            If original(i).key = update(j).key Then
                found = True
                Exit For
            End If
        Next j
        If Not found Then
            result(index) = original(i)
            index += 1
        End If
    Next i
End Sub

Dim As Dictionary original(2)
original(0).key = "name": original(0).value = "Rocket Skates"
original(1).key = "price": original(1).value = "12.75"
original(2).key = "color": original(2).value = "yellow"

Dim As Dictionary update(2)
update(0).key = "price": update(0).value = "15.25"
update(1).key = "color": update(1).value = "red"
update(2).key = "year": update(2).value = "1974"

Dim As Dictionary merged(Ubound(update) + Ubound(original) - 1)
merge(original(), update(), merged())

For i As Integer = 0 To Ubound(merged)
    Print "key: "; merged(i).key; ", value: "; merged(i).value
Next i

Sleep

Output:

key: price, value: 15.25
key: color, value: red
key: year, value: 1974
key: name, value: Rocket Skates

GW-BASIC

Works with: PC-BASIC version any

Works with: BASICA

Works with: QBasic

Works with: MSX BASIC

100 CLS
110 DIM O$(3,2)
120 O$(0,0) = "name"
130 O$(0,1) = "Rocket Skates"
140 O$(1,0) = "price"
150 O$(1,1) = "12.75"
160 O$(2,0) = "color"
170 O$(2,1) = "yellow"
180 DIM U$(3,2)
190 U$(0,0) = "price"
200 U$(0,1) = "15.25"
210 U$(1,0) = "color"
220 U$(1,1) = "red"
230 U$(2,0) = "year"
240 U$(2,1) = "1974"
250 DIM M$(6,2)
270 FOR I = 0 TO 2
280   M$(I,0) = U$(I,0)
290   M$(I,1) = U$(I,1)
300 NEXT I
320 INDEX = 3
330 FOR I = 0 TO 2
340   FOUND = 0
350   FOR J = 0 TO 2
360     IF O$(I,0) = U$(J,0) THEN FOUND = 1 : GOTO 370
370   NEXT J
380   IF FOUND = 0 THEN M$(INDEX,0) = O$(I,0) : M$(INDEX,1) = O$(I,1) : INDEX = INDEX+1
390 NEXT I
410 FOR I = 0 TO INDEX-1
420   PRINT "key: ";M$(I,0);", value: ";M$(I,1)
430 NEXT I
440 END

MSX Basic

Works with: MSX BASIC version any

The GW-BASIC solution works without any changes.

QBasic

Works with: QBasic version 1.1

Works with: QuickBasic version 4.5

Works with: QB64

DECLARE SUB merge (original() AS ANY, update() AS ANY, result() AS ANY)

TYPE Dictionary
    keyy AS STRING * 5
    value AS STRING * 13
END TYPE

DIM original(2) AS Dictionary
original(0).keyy = "name": original(0).value = "Rocket Skates"
original(1).keyy = "price": original(1).value = "12.75"
original(2).keyy = "color": original(2).value = "yellow"

DIM update(2) AS Dictionary
update(0).keyy = "price": update(0).value = "15.25"
update(1).keyy = "color": update(1).value = "red"
update(2).keyy = "year": update(2).value = "1974"

DIM merged(UBOUND(update) + UBOUND(original) - 1) AS Dictionary
CALL merge(original(), update(), merged())

FOR i = 0 TO UBOUND(merged)
    PRINT "keyy: "; merged(i).keyy; ", value: "; merged(i).value
NEXT i
END

SUB merge (original() AS Dictionary, update() AS Dictionary, result() AS Dictionary)
    DIM i AS INTEGER, j AS INTEGER, index AS INTEGER, found AS INTEGER

    FOR i = 0 TO UBOUND(update)
        result(i) = update(i)
    NEXT i

    index = i
    FOR i = 0 TO UBOUND(original)
        found = 0
        FOR j = 0 TO UBOUND(update)
            IF original(i).keyy = update(j).keyy THEN
                found = 1
                EXIT FOR
            END IF
        NEXT j
        IF found = 0 THEN
            result(index) = original(i)
            index = index + 1
        END IF
    NEXT i
END SUB

QB64

The QBasic solution works without any changes.

XBasic

Works with: Windows XBasic

PROGRAM	"Associative array/Merging"
VERSION	"0.0000"

DECLARE FUNCTION Entry ()

FUNCTION Entry ()
    DIM original$[3, 2]
    original$[0, 0] = "name": original$[0, 1] = "Rocket Skates"
    original$[1, 0] = "price": original$[1, 1] = "12.75"
    original$[2, 0] = "color": original$[2, 1] = "yellow"

    DIM update$[3, 2]
    update$[0, 0] = "price": update$[0, 1] = "15.25"
    update$[1, 0] = "color": update$[1, 1] = "red"
    update$[2, 0] = "year": update$[2, 1] = "1974"

    DIM merged$[6, 2]

    FOR i = 0 TO 2
        merged$[i, 0] = update$[i, 0]
        merged$[i, 1] = update$[i, 1]
    NEXT i

    index = 3
    FOR i = 0 TO 2
        found = 0
        FOR j = 0 TO 2
            IF original$[i, 0] = update$[j, 0] THEN
                found = 1
                EXIT FOR
            END IF
        NEXT j
        IF found = 0 THEN
            merged$[index, 0] = original$[i, 0]
            merged$[index, 1] = original$[i, 1]
            INC index
        END IF
    NEXT i

    FOR i = 0 TO index - 1
        PRINT "key: "; merged$[i, 0]; ", value: "; merged$[i, 1]
    NEXT i
END FUNCTION
END PROGRAM

Output:

Same as FreeBASIC entry.

Yabasic

Translation of: FreeBASIC

dim original$(3, 2)
original$(0, 0) = "name"
original$(0, 1) = "Rocket Skates"
original$(1, 0) = "price"
original$(1, 1) = "12.75"
original$(2, 0) = "color"
original$(2, 1) = "yellow"

dim update$(3, 2)
update$(0, 0) = "price"
update$(0, 1) = "15.25"
update$(1, 0) = "color"
update$(1, 1) = "red"
update$(2, 0) = "year"
update$(2, 1) = "1974"

dim merged$(6, 2)

for i = 0 to 2
    merged$(i, 0) = update$(i, 0)
    merged$(i, 1) = update$(i, 1)
next i

index = 3
for i = 0 to 2
    found = 0
    for j = 0 to 2
        if original$(i, 0) = update$(j, 0) then
            found = 1
            break
        end if
    next j
    if found = 0 then
        merged$(index, 0) = original$(i, 0)
        merged$(index, 1) = original$(i, 1)
        index = index + 1
    end if
next i

for i = 0 to index - 1
    print "key: ", merged$(i, 0), ", value: ", merged$(i, 1)
next i

Output:

Same as FreeBASIC entry.

C++

#include <iostream>
#include <string>
#include <map>

template<typename map_type>
map_type merge(const map_type& original, const map_type& update) {
    map_type result(update);
    result.insert(original.begin(), original.end());
    return result;
}

int main() {
    typedef std::map<std::string, std::string> map;
    map original{
        {"name", "Rocket Skates"},
        {"price", "12.75"},
        {"color", "yellow"}
    };
    map update{
        {"price", "15.25"},
        {"color", "red"},
        {"year", "1974"}
    };
    map merged(merge(original, update));
    for (auto&& i : merged)
        std::cout << "key: " << i.first << ", value: " << i.second << '\n';
    return 0;
}

Output:

key: color, value: red
key: name, value: Rocket Skates
key: price, value: 15.25
key: year, value: 1974

C#

using System;
using System.Collections.Generic;
using System.Linq;

public class Program
{
    public static void Main() {
        var baseData = new Dictionary<string, object> {
            ["name"] = "Rocket Skates",
            ["price"] = 12.75,
            ["color"] = "yellow"
        };
        var updateData = new Dictionary<string, object> {
            ["price"] = 15.25,
            ["color"] = "red",
            ["year"] = 1974
        };
        var mergedData = new Dictionary<string, object>();
        foreach (var entry in baseData.Concat(updateData)) {
            mergedData[entry.Key] = entry.Value;
        }
        foreach (var entry in mergedData) {
            Console.WriteLine(entry);
        }
   }
}

Output:

[name, Rocket Skates]
[price, 15.25]
[color, red]
[year, 1974]

Clojure

(defn update-map [base update]
  (merge base update))

  (update-map {"name"  "Rocket Skates"
               "price" "12.75"
               "color" "yellow"}
              {"price" "15.25"
               "color" "red"
               "year"  "1974"})

Output:

{"name" "Rocket Skates", "price" "15.25", "color" "red", "year" "1974"}

Crystal

base = {"name" => "Rocket Skates", "price" => 12.75, "color" => "yellow"}
update = { "price" => 15.25, "color" => "red", "year" => 1974 }

puts base.merge(update)

Output:

{"name" => "Rocket Skates", "price" => 15.25, "color" => "red", "year" => 1974}

Common Lisp

In Common Lisp, the value of a key in an alist or a plist is defined as the first value in the list with a matching key or indicator. Thus, all that is necessary to implement this algorithm for either is the following:

(append list2 list1)

These implementations for alists and plists are more complicated, but avoid duplicate keys in the results:

(defun merge-alists (alist1 alist2)
  (nconc
   (loop :for pair1 :in alist1
         :for pair2 := (assoc (car pair1) alist2)
         :do (setf alist2 (remove pair2 alist2))
         :collect (or pair2 pair1))
   alist2))

(defun merge-plists (plist1 plist2)
  (let ((res '()))
    (loop :for (key val) :on plist1 :by #'cddr
          :do (setf (getf res key) val))
    (loop :for (key val) :on plist2 :by #'cddr
          :do (setf (getf res key) val))
    res))

Dart

main() {
	var base = {
		'name':   'Rocket Skates',
		'price':  12.75,
		'color':  'yellow'
	};

	var newData = {
		'price': 15.25,
		'color': 'red',
		'year':  1974
	};

	var updated = Map.from( base ) // create new Map from base
		..addAll( newData ); // use cascade operator to add all new data
	
	assert( base.toString()    == '{name: Rocket Skates, price: 12.75, color: yellow}' );
	assert( updated.toString() == '{name: Rocket Skates, price: 15.25, color: red, year: 1974}');


}

Delphi

Library: System.Generics.Collections

Translation of: C#

program Associative_arrayMerging;

{$APPTYPE CONSOLE}

uses
  System.Generics.Collections;

type
  TData = TDictionary<string, Variant>;

var
  baseData, updateData, mergedData: TData;
  entry: string;

begin
  baseData := TData.Create();
  baseData.Add('name', 'Rocket Skates');
  baseData.Add('price', 12.75);
  baseData.Add('color', 'yellow');

  updateData := TData.Create();
  updateData.Add('price', 15.25);
  updateData.Add('color', 'red');
  updateData.Add('year', 1974);

  mergedData := TData.Create();
  for entry in baseData.Keys do
    mergedData.AddOrSetValue(entry, baseData[entry]);

  for entry in updateData.Keys do
    mergedData.AddOrSetValue(entry, updateData[entry]);

  for entry in mergedData.Keys do
    Writeln(entry, ' ', mergedData[entry]);

  mergedData.Free;
  updateData.Free;
  baseData.Free;

  Readln;
end.

Output:

price 15,25
year 1974
color red
name Rocket Skates

EasyLang

base$[][] = [ [ "name" "Rocket Skates" ] [ "price" 12.75 ] [ "color" "yellow" ] ]
update$[][] = [ [ "price" 15.25 ] [ "color" "red" ] [ "year" 1974 ] ]
proc update . a$[][] b$[][] .
   for b to len b$[][]
      for a to len a$[][]
         if a$[a][1] = b$[b][1]
            a$[a][2] = b$[b][2]
            break 1
         .
      .
      if a > len a$[][]
         a$[][] &= b$[b][]
      .
   .
.
update base$[][] update$[][]
print base$[][]

Output:

[
 [ "name" "Rocket Skates" ]
 [ "price" "15.25" ]
 [ "color" "red" ]
 [ "year" "1974" ]
]

Elixir

Elixir has a built-in hashmap type, called Map.

base = %{name: "Rocket Skates", price: 12.75, color: "yellow"}
update = %{price: 15.25, color: "red", year: 1974}
result = Map.merge(base, update)
IO.inspect(result)

Output:

%{color: "red", name: "Rocket Skates", price: 15.25, year: 1974}

The above sample uses atoms as the key type. If strings are needed, the base map would look like this:

base = %{"name" => "Rocket Skates", "price" => 12.75, "color" => "yellow"}

F#

type N = |Price of float|Name of string|Year of int|Colour of string
let n=Map<string,N>[("name",Name("Rocket Skates"));("price",Price(12.75));("colour",Colour("yellow"))]
let g=Map<string,N>[("price",Price(15.25));("colour",Colour("red"));("year",Year(1974))]
let ng=(Map.toList n)@(Map.toList g)|>Map.ofList
printfn "%A" ng

Output:

map
  [("colour", Colour "red"); ("name", Name "Rocket Skates");
   ("price", Price 15.25); ("year", Year 1974)]

// Minimum positive multiple in base 10 using only 0 and 1. Nigel Galloway: March 9th., 2020

Factor

The assoc-union word does this. assoc-union! is a variant that mutates the first associative array.

Works with: Factor version 0.99 2019-10-06

USING: assocs prettyprint ;

{ { "name" "Rocket Skates" } { "price" 12.75 } { "color" "yellow" } }
{ { "price" 15.25 } { "color" "red" } { "year" 1974 } }
assoc-union .

Output:

V{
    { "name" "Rocket Skates" }
    { "price" 15.25 }
    { "color" "red" }
    { "year" 1974 }
}

FutureBasic

void local fn DoIt
  CFDictionaryRef base = @{@"name" :@"Rocket Skates", @"price":@12.75, @"color":@"yellow"}
  CFDictionaryRef update = @{@"price":@15.25, @"color":@"red", @"year":@1974}
  
  CFMutableDictionaryRef merged = fn MutableDictionaryWithDictionary( base )
  MutableDictionaryAddEntriesFromDictionary( merged, update )
  
  print merged
end fn

fn DoIt

HandleEvents

This option uses FB's 'concat' function

void local fn Doit
  CFDictionaryRef base = @{ @"name":@"Rocket Skates", @"price":@12.75 }
  CFDictionaryRef update = @{ @"price":@15.25, @"color":@"red", @"year":@1974 }
  CFDictionaryRef result = concat( base, update )
  print result
end fn

fn DoIt

HandleEvents

Output:

{
    color = red;
    name = "Rocket Skates";
    price = "15.25";
    year = 1974;
}

Go

package main

import "fmt"

type assoc map[string]interface{}

func merge(base, update assoc) assoc {
    result := make(assoc)
    for k, v := range base {
        result[k] = v
    }
    for k, v := range update {
        result[k] = v
    }
    return result
}

func main() {
    base := assoc{"name": "Rocket Skates", "price": 12.75, "color": "yellow"}
    update := assoc{"price": 15.25, "color": "red", "year": 1974}
    result := merge(base, update)
    fmt.Println(result)
}

Output:

map[color:red name:Rocket Skates price:15.25 year:1974]

Haskell

There are various approaches, all of which would be strictly typed.
For example, if we want to treat the input and output records as all sharing the same type:

data Item = Item
  { name :: Maybe String
  , price :: Maybe Float
  , color :: Maybe String
  , year :: Maybe Int
  } deriving (Show)

itemFromMerge :: Item -> Item -> Item
itemFromMerge (Item n p c y) (Item n1 p1 c1 y1) =
  Item (maybe n pure n1) (maybe p pure p1) (maybe c pure c1) (maybe y pure y1)

main :: IO ()
main =
  print $
  itemFromMerge
    (Item (Just "Rocket Skates") (Just 12.75) (Just "yellow") Nothing)
    (Item Nothing (Just 15.25) (Just "red") (Just 1974))

Output:

Item {name = Just "Rocket Skates", price = Just 15.25, color = Just "red", year = Just 1974}

Icon and Unicon

procedure main()
    local base, update, master, f, k

    base := table()
    base["name"] := "Rocket Skates"
    base["price"] := 12.75
    base["color"] := "yellow"

    update := table()
    update["price"] := 15.25
    update["color"] := "red"
    update["year"] := 1974

    master := table()
    every k := key((f := base | update)) do {
        master[k] := f[k]
    }

    every k := key(master) do {
        write(k, " = ", master[k])
    }
end

Output:

prompt$ unicon -s merge.icn -x
color = red
name = Rocket Skates
price = 15.25
year = 1974

J

merge=: ,.    NB. use: update merge original
compress=: #"1~ ~:@:keys
keys=: {.
values=: {:
get=: [: > ((i.~ keys)~ <)~ { values@:]   NB. key get (associative array)
pair=: [: |: <;._2;._2

Exercise the definitions. Interactive J prompts with 3 space indentation.

   ] D=: pair 0 :0
name;Rocket Skates;
price;12.75;
color;yellow;
)
┌─────────────┬─────┬──────┐
│name         │price│color │
├─────────────┼─────┼──────┤
│Rocket Skates│12.75│yellow│
└─────────────┴─────┴──────┘

   E=: pair 0 :0
price;15.25;
color;red;
year;1974;
)

   'color'get D
yellow

   'color'get E
red

   ] F=: E merge D
┌─────┬─────┬────┬─────────────┬─────┬──────┐
│price│color│year│name         │price│color │
├─────┼─────┼────┼─────────────┼─────┼──────┤
│15.25│red  │1974│Rocket Skates│12.75│yellow│
└─────┴─────┴────┴─────────────┴─────┴──────┘

   'color' get F
red

   ]G=: compress F
┌─────┬─────┬────┬─────────────┐
│price│color│year│name         │
├─────┼─────┼────┼─────────────┤
│15.25│red  │1974│Rocket Skates│
└─────┴─────┴────┴─────────────┘

   'no such key'get F
|index error: get
|   'no such key'    get F

   'color'get F
red

Java

This task illustrates the difference between statically typed languages, and dynamically typed.
With exception to the var keyword, Java is statically typed. So, using an undefined, non-static, value, creates a trivial situation.

A good way to understand this task is that it's not possible in a static-typed language.
It defeats the purpose of defining the data-type.
For Java, if you're going to use Object as your data-type, you need to re-evaluate the method of abstraction.

Java offers generics, interfaces, and abstract classes for this task.

Considering this, to complete this specific task, I would just store the values as strings.

import java.util.LinkedHashMap;
import java.util.Map;

Map<String, String> mapA = new LinkedHashMap<>();
mapA.put("name", "Rocket Skates");
mapA.put("price", "12.75");
mapA.put("color", "yellow");

Map<String, String> mapB = new LinkedHashMap<>();
mapB.put("price", "15.25");
mapB.put("color", "red");
mapB.put("year", "1974");

Map<String, String> mapC = new LinkedHashMap<>();
mapC.putAll(mapA);
mapC.putAll(mapB);

To show that the original maps are not affected.

for(Map.Entry<String, String> entry : mapA.entrySet())
    System.out.printf("%-20s%s%n", entry.getKey(), entry.getValue());

for(Map.Entry<String, String> entry : mapB.entrySet())
    System.out.printf("%-20s%s%n", entry.getKey(), entry.getValue());

for(Map.Entry<String, String> entry : mapC.entrySet())
    System.out.printf("%-20s%s%n", entry.getKey(), entry.getValue());

name                Rocket Skates
price               12.75
color               yellow

price               15.25
color               red
year                1974

name                Rocket Skates
price               15.25
color               red
year                1974

While not recommended, due to scalability, if you did want to use an Object as the value, you could use the following implementation.
This will produce the same output as above.

Map<String, Object> mapA = new LinkedHashMap<>();
mapA.put("name", "Rocket Skates");
mapA.put("price", 12.75);
mapA.put("color", "yellow");

Map<String, Object> mapB = new LinkedHashMap<>();
mapB.put("price", 15.25);
mapB.put("color", "red");
mapB.put("year", 1974);

Map<String, Object> mapC = new LinkedHashMap<>();
mapC.putAll(mapA);
mapC.putAll(mapB);

JavaScript

(() => {
    'use strict';

    console.log(JSON.stringify(
        Object.assign({}, // Fresh dictionary.
            { // Base.
                "name": "Rocket Skates",
                "price": 12.75,
                "color": "yellow"
            }, { // Update.
                "price": 15.25,
                "color": "red",
                "year": 1974
            }
        ), 
        null, 2
    ))
})();

Output:

{
  "name": "Rocket Skates",
  "price": 15.25,
  "color": "red",
  "year": 1974
}

jq

Mapping “associative array” to “JSON object” in the natural way, the specified operation corresponds exactly to addition in jq, so that if A and B are the first and second objects respectively, then the jq expression `A + B` will yield the required result (as a JSON object).

Julia

julia> dict1 = Dict("name" => "Rocket Skates", "price" => 12.75, "color" => "yellow")
Dict{String,Any} with 3 entries:
  "name"  => "Rocket Skates"
  "price" => 12.75
  "color" => "yellow"

julia> dict2 = Dict("price" => 15.25, "color" => "red", "year" => 1974)
Dict{String,Any} with 3 entries:
  "price" => 15.25
  "year"  => 1974
  "color" => "red"

julia> merge(dict1, dict2)
Dict{String,Any} with 4 entries:
  "name"  => "Rocket Skates"
  "price" => 15.25
  "year"  => 1974
  "color" => "red"

julia> merge(dict2, dict1)
Dict{String,Any} with 4 entries:
  "name"  => "Rocket Skates"
  "price" => 12.75
  "year"  => 1974
  "color" => "yellow"

julia> union(dict1, dict2)
6-element Array{Pair{String,Any},1}:
  "name" => "Rocket Skates"
 "price" => 12.75
 "color" => "yellow"
 "price" => 15.25
  "year" => 1974
 "color" => "red"

Kotlin

fun main() {
    val base = HashMap<String,String>()
    val update =  HashMap<String,String>()

    base["name"] = "Rocket Skates"
    base["price"] = "12.75"
    base["color"] = "yellow"

    update["price"] = "15.25"
    update["color"] = "red"
    update["year"] = "1974"

    val merged = HashMap(base)
    merged.putAll(update)

    println("base: $base")
    println("update: $update")
    println("merged: $merged")
}

Output:

base: {color=yellow, price=12.75, name=Rocket Skates}
update: {color=red, year=1974, price=15.25}
merged: {name=Rocket Skates, color=red, year=1974, price=15.25}

Lua

base = {name="Rocket Skates", price=12.75, color="yellow"}
update = {price=15.25, color="red", year=1974}

--[[ clone the base data ]]--
result = {}
for key,val in pairs(base) do
    result[key] = val
end

--[[ copy in the update data ]]--
for key,val in pairs(update) do
    result[key] = val
end

--[[ print the result ]]--
for key,val in pairs(result) do
    print(string.format("%s: %s", key, val))
end

Output:

price: 15.25
color: red
year: 1974
name: Rocket Skates

Mathematica / Wolfram Language

a1 = <|"name" -> "Rocket Skates", "price" -> 12.75, "color" -> "yellow"|>;
a2 = <|"price" -> 15.25, "color" -> "red", "year" -> 1974|>;
Merge[{a1, a2}, Last]

Output:

<|"name" -> "Rocket Skates", "price" -> 15.25, "color" -> "red", "year" -> 1974|>

MiniScript

MiniScript supports merging maps with the + operator.

base = {"name":"Rocket Skates", "price":12.75, "color":"yellow"}
update = {"price":15.25, "color":"red", "year":1974}

result = base + update

print result

Output:

{"color": "red", "name": "Rocket Skates", "price": 15.25, "year": 1974}

newLISP

Let's use simple association lists.

(setq data1 '("name" "Rocket Skates"
            "price" 12.75
            "color" "yellow"))

(setq data2 '("price" 	15.25
          "color" 	"red"
          "year" 	1974))

(define (list->alist lst)  (explode lst 2))

(macro (aset! Alist Key Val)
  (local (E-Message)
    (unless  
      (catch
        (setf (assoc Key Alist) (list ($it 0) Val))
        'E-Message)
      (setf Alist (cons (list Key Val) Alist)))))

(define (foo list1 list2)
  (let (out (list->alist list1))
    (dolist (a (list->alist list2))
      (aset! out (a 0) (string (a 1))))
    (println out "\n")
    (dolist (a out)
      (println (format "%-5s  %s" a)))))

(foo data1 data2)

Output:

(("year" "1974") ("name" "Rocket Skates") ("price" "15.25") ("color" "red"))

year   1974
name   Rocket Skates
price  15.25
color  red

Let's make it more interesting. The "color" field will be a list of colors; the color from the new array will be appended to what's already in the field.

Also, the price in the second associative array will be added to the original price.

(setq data1 '("name" "Rocket Skates"
            "price" 12.75
            "color" "yellow"))

(setq data2 '("price" 	3.20
          "color" 	"red"
          "year" 	1974))

(macro (ainc! Alist Key Val Func)
  (local (E-Message)
    (unless Func (set 'Func +))
    (unless  
      (catch
        (setf (assoc Key Alist)
          (list ($it 0) (Func (or Val 1) ($it 1))))
        'E-Message)
      (setf Alist (cons (list Key (or Val 1)) Alist)))))

(define (list->alist xs)
  (collect
    (and (true? xs)
      (if (= "color" (xs 0))
        (list (pop xs) (list (pop xs)))
        (list (pop xs) (pop xs))))))

(define (bu) (bind (apply unify $args)))

(define (foo list1 list2   , K V)
  (let (out (list->alist list1))
    (dolist (a (list->alist list2))
      (bu '(K V) a)
      (case K
        ("price" (ainc! out K V add))
        ("color" (ainc! out K V append))
        ;; ainc! can even be used to make a new entry or replace old value.
        (true    (ainc! out K V or))))
    (println out "\n")
    (dolist (a out)
      (bu '(K V) a)
      (println (format "%-5s  " K) V))))

(foo data1 data2)

Output:

(("year" 1974) ("name" "Rocket Skates") ("price" 15.95)
 ("color" ("red" "yellow")))

year   1974
name   Rocket Skates
price  15.95
color  ("red" "yellow")

Nim

import tables

let t1 = {"name": "Rocket Skates", "price": "12.75", "color": "yellow"}.toTable
let t2 = {"price": "15.25", "color": "red", "year": "1974"}.toTable

var t3 = t1   # Makes a copy.
for key, value in t2.pairs:
  t3[key] = value

echo t3

Output:

{"name": "Rocket Skates", "year": "1974", "color": "red", "price": "15.25"}

Nu

Works with: Nushell version 0.96.1

const base = {name: 'Rocket Skates' price: 12.75 color: 'yellow'}
const update = {price: 15.25 color: 'red' year: 1974}

$base | merge $update

Output:

╭───────┬───────────────╮
│ name  │ Rocket Skates │
│ price │ 15.25         │
│ color │ red           │
│ year  │ 1974          │
╰───────┴───────────────╯

Objective-C

Works with: Cocoa

#import <Foundation/Foundation.h>

int main(void) {
  @autoreleasepool {
    NSDictionary *base = @{@"name": @"Rocket Skates", @"price": @12.75, @"color": @"yellow"};
    NSDictionary *update = @{@"price": @15.25, @"color": @"red", @"year": @1974};
    
    NSMutableDictionary *result = [[NSMutableDictionary alloc] initWithDictionary:base];
    [result addEntriesFromDictionary:update];
    
    NSLog(@"%@", result);
  }
  return 0;
}

Output:

{
    color = red;
    name = "Rocket Skates";
    price = "15.25";
    year = 1974;
}

OCaml

Original version by User:Vanyamil

Note that, given OCaml's strong typing, we must declare a type here for the 3-type data. In general, would need the specific data type for the task, or use a PPX rewriter (effectively a compiler middleware) that can rewrite code based on dynamic type extensions.

Helper code for all 3 versions:

type ty = 
    | TFloat of float
    | TInt of int
    | TString of string

type key = string
type assoc = string * ty

let string_of_ty : ty -> string = function
    | TFloat x -> string_of_float x
    | TInt i -> string_of_int i
    | TString s -> s

let print_pair key el =
    Printf.printf "%s: %s\n" key (string_of_ty el)
;;

Association list : naive and functional approach.

let l1 : assoc list = [
    ("name", TString "Rocket Skates");
    ("price", TFloat 12.75);
    ("color", TString "yellow")
] ;;

let l2 : assoc list = [
    ("price", TFloat 15.25);
    ("color", TString "red");
    ("year",  TInt 1974)
] ;;

let rec merge_assoc_list (base_list : assoc list) (add_list : assoc list) : assoc list = 
    List.fold_left
        (fun l (key, val_) -> 
            (key, val_) :: (List.remove_assoc key l)
        )
        base_list
        add_list
;;

let l' = merge_assoc_list l1 l2 ;;

Binary tree/Map functor : proper functional approach.

Works with: OCaml version above 4.03 for union function

module StringMap = Map.Make(String) ;;

let print_map = StringMap.iter print_pair ;;

let map_merge (base : ty StringMap.t) (add : ty StringMap.t) : ty StringMap.t = 
    StringMap.union (fun key v1 v2 -> Some v2) base add
;;

let m1 = StringMap.(
    empty 
    |> add "name" (TString "Rocket Skates")
    |> add "price" (TFloat 12.75)
    |> add "color" (TString "yellow")
) ;;

let m2 = StringMap.(
    empty 
    |> add "price" (TFloat 15.25)
    |> add "color" (TString "red")
    |> add "year" (TInt 1974)
) ;;

let m' = map_merge m1 m2 ;;

print_map m' ;;

Hash table : imperative/mutable approach.

(* Updates the base table with the bindings from add *)
let hash_merge (base : (string, ty) Hashtbl.t) (add : (string, ty) Hashtbl.t) : unit = 
    Hashtbl.iter (Hashtbl.replace base) add

let print_hashtbl t =
    Hashtbl.iter print_pair t

let h1 : (string, ty) Hashtbl.t = Hashtbl.create 10 ;;
Hashtbl.add h1 "name" (TString "Rocket Skates") ;;
Hashtbl.add h1 "price" (TFloat 12.75) ;;
Hashtbl.add h1 "color" (TString "yellow") ;;

let h2 : (string, ty) Hashtbl.t = Hashtbl.create 10 ;;
Hashtbl.add h2 "price" (TFloat 15.25) ;;
Hashtbl.add h2 "color" (TString "red") ;;
Hashtbl.add h2 "year" (TInt 1974) ;;

hash_merge h1 h2 ;;

print_hashtbl h1 ;;

Ol

Since version 3.1.1 function `ff-union` changed from `(ff-union a1 a2 collide)` to `(ff-union collide a1 a2 ...)`!

(define a1 {
   'name    "Rocket Skates"
   'price   12.75
   'color   "yellow"
})

(define a2 {
   'price   15.25
   'color   "red"
   'year    1974 
})

(print "a1: " a1)
(print "a2: " a2)

(define (collide a b) b) ; will use new key value
(print "merged a1 a2: " (ff-union collide a1 a2))

Output:

a1: #ff((name . Rocket Skates) (price . 51/4) (color . yellow))
a2: #ff((price . 61/4) (color . red) (year . 1974))
merged a1 a2: #ff((name . Rocket Skates) (price . 61/4) (color . red) (year . 1974))

PascalABC.NET

begin
  var base := Dict(('name','Rocket Skates'),
    ('price','12.75'),
    ('color','yellow'));
  
  var update := Dict(('price','15.25'),
    ('color','red'),
    ('year','1974'));
    
  var merged := new Dictionary<string,string>;
  foreach var kv in base.Concat(update) do
    merged[kv.Key] := kv.Value;
  merged.PrintLines
end.

Output:

(name,Rocket Skates)
(price,15.25)
(color,red)
(year,1974)

Perl

use strict;
use warnings;

my %base = ("name" => "Rocket Skates", "price" => 12.75, "color" => "yellow");
my %more = ("price" => 15.25, "color" => "red", "year" => 1974);

print "Update\n";
my %update = (%base, %more);
printf "%-7s %s\n", $_, $update{$_} for sort keys %update;

print "\nMerge\n";
my %merge;
$merge{$_} = [$base{$_}] for keys %base;
push @{$merge{$_}}, $more{$_} for keys %more;
printf "%-7s %s\n", $_, join ', ', @{$merge{$_}} for sort keys %merge;

Output:

Update
color   red
name    Rocket Skates
price   15.25
year    1974

Merge
color   yellow, red
name    Rocket Skates
price   12.75, 15.25
year    1974

Phix

with javascript_semantics
integer d1 = new_dict({{"name","Rocket Skates"},{"price",12.75},{"color","yellow"}}),
        d2 = new_dict({{"price",15.25},{"color","red"},{"year",1974}}),
        d3 = new_dict(d1)
function merger(object key, data, /*user_data*/) setd(key,data,d3) return 1 end function
traverse_dict(merger,NULL,d2)
include builtins/map.e
?pairs(d3)

Output:

{{"color","red"},{"name","Rocket Skates"},{"price",15.25},{"year",1974}}

Phixmonti

include ..\Utilitys.pmt

def scand   /# dict key -- dict n #/
    0 var flag
    var ikey
    len for
        var i
        i 1 2 tolist sget
        ikey == if i var flag exitfor endif
    endfor
    flag
enddef


def getd    /# dict key -- dict data #/
    scand
    dup if get 2 get nip else drop "Unfound" endif
enddef


def setd    /# dict ( key data ) -- dict #/
    1 get rot swap
    scand
    rot swap
    dup if set else put endif
enddef

/# ---------- MAIN ---------- #/

( ( "name" "Rocket Skates" )
  ( "price" 12.75 )
  ( "color" "yellow" ) )

dup
  
( ( "price" 15.25 )
  ( "color" "red" )
  ( "year" 1974 ) )
  
len for
    get rot swap setd swap
endfor

swap

pstack

PHP

<?
$base = array("name" => "Rocket Skates", "price" => 12.75, "color" => "yellow");
$update = array("price" => 15.25, "color" => "red", "year" => 1974);

$result = $update + $base; // Notice that the order is reversed
print_r($result);
?>

Output:

Array
(
    [price] => 15.25
    [color] => red
    [year] => 1974
    [name] => Rocket Skates
)

Alternative:

<?
$base = array("name" => "Rocket Skates", "price" => 12.75, "color" => "yellow");
$update = array("price" => 15.25, "color" => "red", "year" => 1974);

$result = array_merge($base, $update);
print_r($result);
?>

Output:

Array
(
    [name] => Rocket Skates
    [price] => 15.25
    [color] => red
    [year] => 1974
)

PureBasic

NewMap m1.s()
NewMap m2.s()
NewMap m3.s()

m1("name")="Rocket Skates"
m1("price")="12.75"
m1("color")="yellow"

m2("price")="15.25"
m2("color")="red"
m2("year")="1974"

CopyMap(m1(),m3())
 
ForEach m2()
  m3(MapKey(m2()))=m2()
Next

ForEach m3()
  Debug MapKey(m3())+" : "+m3()
Next

Output:

price : 15.25
color : red
year : 1974
name : Rocket Skates

Python

As of Python 3.5, this can be solved with the dictionary unpacking operator.

Works with: Python version 3.5+

base = {"name":"Rocket Skates", "price":12.75, "color":"yellow"}
update = {"price":15.25, "color":"red", "year":1974}

result = {**base, **update}

print(result)

Output:

{'name': 'Rocket Skates', 'price': 15.25, 'color': 'red', 'year': 1974}

Alternative

base = {"name":"Rocket Skates", "price":12.75, "color":"yellow"}
update = {"price":15.25, "color":"red", "year":1974}

result = base.copy()
result.update(update)

print(result)

Output:

{'name': 'Rocket Skates', 'price': 15.25, 'color': 'red', 'year': 1974}

New alternative using '|'

Python 3.9.0 (tags/v3.9.0:9cf6752, Oct  5 2020, 15:34:40) [MSC v.1927 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license()" for more information.
>>> base = {"name":"Rocket Skates", "price":12.75, "color":"yellow"}
>>> update = {"price":15.25, "color":"red", "year":1974}
>>> result = base | update
>>> result
{'name': 'Rocket Skates', 'price': 15.25, 'color': 'red', 'year': 1974}
>>>

Racket

#lang racket/base

(require racket/hash)

(module+ test
  (require rackunit)

  (define base-data (hash "name"	"Rocket Skates"
                          "price"	12.75
                          "color"	"yellow"))

  (define update-data (hash "price"	15.25
                            "color"	"red"
                            "year"	1974))

  (hash-union base-data update-data #:combine (λ (a b) b)))

Output:

'#hash(("color" . "red") ("name" . "Rocket Skates") ("price" . 15.25) ("year" . 1974))

Raku

(formerly Perl 6)

Works with: Rakudo version 2019.11

I must say I somewhat disagree with the terminology. The requested operation is an update not a merge. Demonstrate both an update and a merge. Associative arrays are commonly called hashes in Raku.

# Show original hashes
say my %base   = :name('Rocket Skates'), :price<12.75>, :color<yellow>;
say my %update = :price<15.25>, :color<red>, :year<1974>;

# Need to assign to anonymous hash to get the desired results and avoid mutating
# TIMTOWTDI
say "\nUpdate:\n", join "\n", sort %=%base, %update;
# Same
say "\nUpdate:\n", {%base, %update}.sort.join: "\n";

say "\nMerge:\n", join "\n", sort ((%=%base).push: %update)».join: ', ';
# Same
say "\nMerge:\n", ({%base}.push: %update)».join(', ').sort.join: "\n";

# Demonstrate unmutated hashes
say "\n", %base, "\n", %update;

Output:

{color => yellow, name => Rocket Skates, price => 12.75}
{color => red, price => 15.25, year => 1974}

Update:
color	red
name	Rocket Skates
price	15.25
year	1974

Update:
color	red
name	Rocket Skates
price	15.25
year	1974

Merge:
color	yellow, red
name	Rocket Skates
price	12.75, 15.25
year	1974

Merge:
color	yellow, red
name	Rocket Skates
price	12.75, 15.25
year	1974

{color => yellow, name => Rocket Skates, price => 12.75}
{color => red, price => 15.25, year => 1974}

REXX

The REXX language has no native support to acquire the keys of an associate array after they have been defined,
so it must be performed at definition time, but there are function packages to perform this function.

Some extra coding was added to support adjustable (maximum) widths for the displaying of the associate array names, keys, and values.

The double quotes that surround the string (character) items (as shown in the task's preamble) weren't included for this presentation,
although they could easily be added.

/*REXX program merges two associative arrays  (requiring an external list of indices).  */
$.=                                              /*define default value(s) for arrays.  */
@.wAAn= 21;      @.wKey= 7;       @.wVal= 7      /*max widths of:  AAname, keys, values.*/
call defAA  'base',     "name Rocket Skates",   'price 12.75',   "color yellow"
call defAA  'update',   "price 15.25",          "color red",     'year 1974'
call show   'base'
call show   'update'
call show   'new'
exit                                             /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
defAA: procedure expose $. @.;  parse arg AAn;      new= 'new'   /*get AA name; set NEW.*/
         do j=2  to arg();   parse value arg(j)  with  key val   /*obtain key and value.*/
         $.AAn.key= val                          /*assign a  value  to a  key for AAn.  */
         if wordpos(key, $.AAN.?keys)==0  then $.AAn.?keys= $.AAn.?keys key
                                                 /* [↑]  add to key list if not in list.*/
         $.new.key= val                          /*assign a  value  to a  key for "new".*/
         if wordpos(key, $.new.?keys)==0  then $.new.?keys= $.new.?keys key
                                                 /* [↑]  add to key list if not in list.*/
         @.wKey= max(@.wKey, length(key) )       /*find max width of a name of a  key.  */
         @.wVal= max(@.wVal, length(val) )       /*  "   "    "    " "   "   " "  value.*/
         @.wAA = max(@.wAAn, length(AAn) )       /*  "   "    "    " "   "   "    array.*/
         end   /*j*/
       return
/*──────────────────────────────────────────────────────────────────────────────────────*/
show:  procedure expose $. @.;  parse arg AAn;      say;     _= '═'    /*set title char.*/
         do j=1  for words($.AAn.?keys)                                /*process keys.  */
         if j==1  then say  center('associate array', @.wAAn,     _)  ,
                            center("key"            , @.wKey,     _)  ,
                            center('value'          , @.wVal + 2, _)
         key= word($.AAn.?keys, j)                              /*get the name of a key.*/
         say center(AAn, @.wAAn)  right(key, @.wKey)  $.AAn.key /*show some information.*/
         end   /*j*/
       return

output when using the internal default inputs:

═══associate array═══ ══key══ ═════value═════
        base             name Rocket Skates
        base            price 12.75
        base            color yellow

═══associate array═══ ══key══ ═════value═════
       update           price 15.25
       update           color red
       update            year 1974

═══associate array═══ ══key══ ═════value═════
         new             name Rocket Skates
         new            price 15.25
         new            color red
         new             year 1974

Ring

load "stdlib.ring"

list1 = [:name = "Rocket Skates", :price = 12.75, :color = "yellow"]
list2 = [:price = 15.25, :color = "red", :year = 1974]

for n = 1 to len(list2)
    flag = 0
    for m = 1 to len(list1)
        if list2[n][1] = list1[m][1]
           flag = 1
           del(list1,m)
           add(list1,[list2[n][1],list2[n][2]])
           exit
        ok
    next
    if flag = 0
       add(list1,[list2[n][1],list2[n][2]])
    ok
next

for n = 1 to len(list1)
    see list1[n][1] + " = " + list1[n][2] + nl
next

Output:

name = Rocket Skates
price = 15.25
color = red
year = 1974

Ruby

base = {"name" => "Rocket Skates", "price" => 12.75, "color" => "yellow"}
update = {"price" => 15.25, "color" => "red", "year" => 1974}

result = base.merge(update)
p result

Output:

{"name"=>"Rocket Skates", "price"=>15.25, "color"=>"red", "year"=>1974}

Rust

use std::collections::HashMap;

fn main() {
    let mut original = HashMap::new();
    original.insert("name", "Rocket Skates");
    original.insert("price", "12.75");
    original.insert("color", "yellow");

    let mut update = HashMap::new();
    update.insert("price", "15.25");
    update.insert("color", "red");
    update.insert("year", "1974");

    original.extend(&update);

    println!("{:#?}", original);
}

Output:

{
    "name": "Rocket Skates",
    "color": "red",
    "year": "1974",
    "price": "15.25",
}

Scheme

Works with: Chez Scheme

Quick and Dirty
The procedures which access association lists (alist) in Scheme prefer the first matched item in an alist. Hence, a merge may be implemented by simply appending the update alist to the front of the base alist. The downside is this leaves a bunch of useless junk in the alist.

; Merge alists by appending the update list onto the front of the base list.
; (The extra '() is so that append doesn't co-opt the second list.)
(define append-alists
  (lambda (base update)
    (append update base '())))

; Test...
(printf "~%Merge using append procedure...~%")
; The original base and update alists.
(let ((base '(("name" . "Rocket Skates") ("price" . 12.75) ("color" . "yellow" )))
      (update '(("price" . 15.25) ("color" . "red") ("year" . 1974))))
  ; Merge by appending the update list onto the front of the base list.
  (let ((merged (append-alists base update)))
    ; Show that everything worked.
    (printf "Merged alist:~%~s~%" merged)
    (printf "Values from merged alist:~%")
    (let loop ((keys '("name" "price" "color" "year")))
      (unless (null? keys)
        (printf "~s -> ~s~%" (car keys) (cdr (assoc (car keys) merged)))
        (loop (cdr keys))))))

Output:

Merge using append procedure...
Merged alist:
(("price" . 15.25) ("color" . "red") ("year" . 1974) ("name" . "Rocket Skates") ("price" . 12.75) ("color" . "yellow"))
Values from merged alist:
"name" -> "Rocket Skates"
"price" -> 15.25
"color" -> "red"
"year" -> 1974

More True to Intent
This is more true to the intent of the Task. It generates a new alist with only the key/value pairs needed.

; Merge the given alists.  Prefer the items from the "update" alist.
; Returns a new list; the argument lists are not modified.
(define merge-alists
  (lambda (base update)
    (let ((merged (list-copy update))
          (remains (list-copy base)))
      (let loop ((shadowing merged))
        (if (null? shadowing)
          (append merged remains)
          (begin (set! remains (remp (lambda (pair) (equal? (car pair) (caar shadowing)))
                                     remains))
                 (loop (cdr shadowing))))))))

; Test...
(printf "~%Merge using defined merge-alists procedure...~%")
; The original base and update alists.
(let ((base '(("name" . "Rocket Skates") ("price" . 12.75) ("color" . "yellow" )))
      (update '(("price" . 15.25) ("color" . "red") ("year" . 1974))))
  ; Merge using the defined merge-alists procedure.
  (let ((merged (merge-alists base update)))
    ; Show that everything worked.
    (printf "Merged alist:~%~s~%" merged)
    (printf "Values from merged alist:~%")
    (let loop ((keys '("name" "price" "color" "year")))
      (unless (null? keys)
        (printf "~s -> ~s~%" (car keys) (cdr (assoc (car keys) merged)))
        (loop (cdr keys))))))

Output:

Merge using defined merge-alists procedure...
Merged alist:
(("price" . 15.25) ("color" . "red") ("year" . 1974) ("name" . "Rocket Skates"))
Values from merged alist:
"name" -> "Rocket Skates"
"price" -> 15.25
"color" -> "red"
"year" -> 1974

SenseTalk

In addition to setting individual property values, SenseTalk includes 5 built-in operations for modifying property lists, to: add properties, replace properties, remove properties, retain properties, and rename properties. The operation to replace properties is needed for this task.

set base to {name:"Rocket Skates", price:12.75, color:"yellow"}

set update to {price:15.25, color:"red", year:1974}

put "Base data: " & base
put "Update data: " & update

// replacing as an operator, to generate merged data on the fly:
put "Merged data: " & base replacing properties in update

// replace as a command, to modify base data in place:
replace properties of update in base
put "Base after update: " & base

Output:

Base data: {color:"yellow", name:"Rocket Skates", price:12.75}
Update data: {color:"red", price:15.25, year:1974}
Merged data: {color:"red", name:"Rocket Skates", price:15.25, year:1974}
Base after update: {color:"red", name:"Rocket Skates", price:15.25, year:1974}

Smalltalk

base := Dictionary withAssociations:{ 
         'name'-> 'Rocket Skates' .
         'price' -> 12.75 .
         'color' -> 'yellow' }.

update := Dictionary withAssociations:{
         'price' -> 15.25 .
         'color' -> 'red' .
         'year' -> 1974 }.
 
result := Dictionary new
             declareAllFrom:base;
             declareAllFrom:update.

Transcript showCR: result.

Output:

Dictionary(name->Rocket Skates price->15.25 year->1974 color->red)

Swift

Works with: Swift version 5+

let base : [String: Any] = ["name": "Rocket Skates", "price": 12.75, "color": "yellow"]
let update : [String: Any] = ["price": 15.25, "color": "red", "year": 1974]

let result = base.merging(update) { (_, new) in new }

print(result)

Output:

["price": 15.25, "name": "Rocket Skates", "color": "red", "year": 1974]

Tcl

set dict1 [dict create name "Rocket Skates" price 12.75 color yellow]
set dict2 [dict create price 15.25 color red year 1974]
dict for {key val} [dict merge $dict1 $dict2] {
    puts "$key: $val"
}

Output:

name: Rocket Skates
price: 15.25
color: red
year: 1974

VBA

3 ways to do this tasks : First : With Arrays + Type

Private Type Associative
    Key As String
    Value As Variant
End Type
Sub Main_Array_Associative()
Dim BaseArray(2) As Associative, UpdateArray(2) As Associative
    FillArrays BaseArray, UpdateArray
    ReDim Result(UBound(BaseArray)) As Associative
    MergeArray Result, BaseArray, UpdateArray
    PrintOut Result
End Sub
Private Sub MergeArray(Res() As Associative, Base() As Associative, Update() As Associative)
Dim i As Long, Respons As Long
    Res = Base
    For i = LBound(Update) To UBound(Update)
        If Exist(Respons, Base, Update(i).Key) Then
            Res(Respons).Value = Update(i).Value
        Else
            ReDim Preserve Res(UBound(Res) + 1)
            Res(UBound(Res)).Key = Update(i).Key
            Res(UBound(Res)).Value = Update(i).Value
        End If
    Next
End Sub
Private Function Exist(R As Long, B() As Associative, K As String) As Boolean
Dim i As Long
    Do
        If B(i).Key = K Then
            Exist = True
            R = i
        End If
        i = i + 1
    Loop While i <= UBound(B) And Not Exist
End Function
Private Sub FillArrays(B() As Associative, U() As Associative)
    B(0).Key = "name"
    B(0).Value = "Rocket Skates"
    B(1).Key = "price"
    B(1).Value = 12.75
    B(2).Key = "color"
    B(2).Value = "yellow"
    U(0).Key = "price"
    U(0).Value = 15.25
    U(1).Key = "color"
    U(1).Value = "red"
    U(2).Key = "year"
    U(2).Value = 1974
End Sub
Private Sub PrintOut(A() As Associative)
Dim i As Long
    Debug.Print "Key", "Value"
    For i = LBound(A) To UBound(A)
        Debug.Print A(i).Key, A(i).Value
    Next i
    Debug.Print "-----------------------------"
End Sub

Second way (simply) : with the Scripting Dictionary Object :

Sub Main_With_Dictionary()
Dim Base As Object, Update As Object, Merged As Object, K As Variant
    'INIT VARIABLE
    Set Base = CreateObject("Scripting.Dictionary")
    Set Update = CreateObject("Scripting.Dictionary")
    Set Merged = Base
    'FILL Base & Update
    Base.Add "name", "Rocket Skates"
    Base.Add "price", 12.75
    Base.Add "color", "yellow"
    Update.Add "price", 15.25
    Update.Add "color", "red"
    Update.Add "year", 1974
    'Fill Merge
    For Each K In Update.Keys
        Merged(K) = Update(K)
    Next
    'Print Out
    Debug.Print "Key", "Value"
    For Each K In Merged.Keys
        Debug.Print K, Merged(K)
    Next K
End Sub

And the Third : With a Class Module (named ClassArrayAssociative) The Class Module code:

Option Explicit

Private mKey As String
Private mValue As Variant

Public Property Get Value() As Variant
    Value = mValue
End Property
Public Property Let Value(iValue As Variant)
    mValue = iValue
End Property
Public Property Get Key() As Variant
    Key = mKey
End Property
Private Property Let Key(iKey As Variant)
    mKey = iKey
End Property

Public Sub Add(K As String, V As Variant)
    Value = V
    Key = K
End Sub

The Module code :

Sub Main_With_Class()
Dim Base(2) As New ClassArrayAssociative, Up(2) As New ClassArrayAssociative
    ReDim Result(UBound(Base)) As New ClassArrayAssociative
    'FILL Base & Update
    Base(0).Add "name", "Rocket Skates"
    Base(1).Add "price", 12.75
    Base(2).Add "color", "yellow"
    Result = Base
    Up(0).Add "price", 15.25
    Up(1).Add "color", "red"
    Up(2).Add "year", 1974
    'Update Result with Up
    Update Result, Up
    'Print Out
    Print_Out_2 Result
End Sub
Private Sub Update(R() As ClassArrayAssociative, U() As ClassArrayAssociative)
Dim i As Long, j As Long, Flag As Boolean
    For i = LBound(U) To UBound(U)
        j = LBound(R)
        Flag = False
        Do While j <= UBound(R) And Not Flag
            If R(j).Key = U(i).Key Then
                R(j).Value = U(i).Value
                Flag = True
            End If
            j = j + 1
        Loop
        If Not Flag Then
            ReDim Preserve R(UBound(R) + 1)
            Set R(UBound(R)) = New ClassArrayAssociative
            R(UBound(R)).Add U(i).Key, U(i).Value
        End If
    Next i
End Sub
Private Sub Print_Out_2(A() As ClassArrayAssociative)
Dim i As Long
    Debug.Print "Key", "Value"
    For i = LBound(A) To UBound(A)
        Debug.Print A(i).Key, A(i).Value
    Next i
    Debug.Print "-----------------------------"
End Sub

Output:

Key           Value
name          Rocket Skates
price          15,25 
color         red
year           1974 
-----------------------------

VBScript

set d1=createobject("Scripting.Dictionary")
d1.add "name", "Rocket Skates"
d1.add "price", 12.75
d1.add "color", "yellow"

set d2=createobject("Scripting.Dictionary")
d2.add "price", 15.25
d2.add "color", "red"
d2.add "year", 1974

set d3=createobject("Scripting.Dictionary")
for each k1 in d1.keys
   if not d3.exists(k1) then
     d3.add k1, d1(k1)
   else
     d3(k1)=d1(k1)
   end if
next	
for each k2 in d2.keys
   if not d3.exists(k2) then
      d3.add k2, d2(k2)
   else
      d3(k2)=d2(k2)
   end if
next	 

for each k3 in d3.keys
   wscript.echo k3 & vbtab & d3(k3)
next

Output:

name    Rocket Skates
price   15.25
color   red
year    1974

V (Vlang)

type Generic = int|string|f64
type Assoc = map[string]Generic

fn merge(base Assoc, update Assoc) Assoc {
    mut result := Assoc(map[string]Generic{})
    for k, v in base {
        result[k] = v
    }
    for k, v in update {
        result[k] = v
    }
    return result
}
 
fn main() {
    base := Assoc({"name": Generic("Rocket Skates"), "price": 12.75, "color": "yellow"})
    update := Assoc({"price": Generic(15.25), "color": "red", "year": 1974})
    result := merge(base, update)
    for k,v in result {
        println('$k: $v')
    }
}

Output:

name: Generic('Rocket Skates')
price: Generic(15.25)
color: Generic('red')
year: Generic(1974)

Wren

var mergeMaps = Fn.new { |m1, m2|
    var m3 = {}
    for (key in m1.keys) m3[key] = m1[key]
    for (key in m2.keys) m3[key] = m2[key]
    return m3
}     

var base = { "name": "Rocket Skates" , "price": 12.75, "color": "yellow" }
var update = { "price": 15.25, "color": "red", "year": 1974 }
var merged = mergeMaps.call(base, update)
System.print(merged)

Output:

{name: Rocket Skates, color: red, price: 15.25, year: 1974}

zkl

base:=Dictionary(
   "name", 	"Rocket Skates",
   "price", 	12.75,
   "color", 	"yellow",);
update:=Dictionary(
   "price", 	15.25,
   "color", 	"red",
   "year", 	1974,);

update.pump( new:=base.copy() );

new.pump(Void,fcn([(k,v)]){ println("%s\t%s".fmt(k,v)) });

Output:

price	15.25
color	red
year	1974
name	Rocket Skates