Tree datastructures: Difference between revisions

From Rosetta Code
Content added Content deleted
(→‎Procedural: golf->troll)
m (Withdrew the examples which use other sample outlines. I don't feel comfortable reproducing jokes about mocking and trolling.)
Line 39: Line 39:


Show all output on this page.
Show all output on this page.

=={{header|AppleScript}}==
{{incorrect|AppleScript|"Strayed" from task example. (Task example updated as you are right).}}
The 'mocking' task example seems a little unpleasant. Perhaps an alternative ?
<lang applescript>use AppleScript version "2.4"
use framework "Foundation"
use scripting additions

on run
set strOutline to ¬
"The Rosetta stone\n" & ¬
" is a granodiorite stele\n" & ¬
" engraved\n" & ¬
" with Greek and Egyptian texts\n" & ¬
" in different scripts.\n" & ¬
" which, in the 19c, shed new light\n" & ¬
" on various homologies."
set forestA to ¬
forestFromNestLevels(indentLevelsFromLines(paragraphs of strOutline))
set indentLevels to nestLevelsFromForest(forestA)
set forestB to forestFromNestLevels(indentLevels)
-- Logged to Messages panel of macOS Script Editor
log intercalate(linefeed & linefeed, {¬
"Outline:", ¬
strOutline, ¬
"Forest from outline:", ¬
forestJSON(forestA), ¬
"Nesting levels from forest:", ¬
toJSON(indentLevels), ¬
"Forest rebuilt from nesting levels", ¬
forestJSON(forestB), ¬
"Equality test:", ¬
"(forestA = forestB) -> " & (forestA = forestB)})
end run

-- TREES ⇄ LEVEL TUPLES ----------------------------------

-- forestFromNestLevels :: [(Int, a)] -> [Tree a]
on forestFromNestLevels(tuples)
-- A list of trees derived from a list of values paired
-- with integers giving their levels of indentation.
script go
on |λ|(xs)
if 0 < length of xs then
set lineOne to item 1 of xs
set {intIndent, v} to {fst(lineOne), snd(lineOne)}
set {firstTreeLines, remainingLines} to ¬
listFromTuple(|λ|(rest of xs) of ¬
span(compose(lt(intIndent), my fst)))
{Node(v, |λ|(firstTreeLines) of go)} & |λ|(remainingLines) of go
else
{}
end if
end |λ|
end script
|λ|(tuples) of go
end forestFromNestLevels


-- nestLevelsFromForest :: [Tree a] -> [(Int, a)]
on nestLevelsFromForest(trees)
-- A flat list of (nest level, value) tuples,
-- representing a series of trees.
script go
on |λ|(level)
script
on |λ|(tree)
{{level, root of tree}} & ¬
concatMap(|λ|(1 + level) of go, nest of tree)
end |λ|
end script
end |λ|
end script
concatMap(|λ|(0) of go, trees)
end nestLevelsFromForest


-- INDENT LEVELS FROM OUTLINE ----------------------------

--indentLevelsFromLines :: [String] -> [(Int, String)]
on indentLevelsFromLines(xs)
set tuples to map(compose(firstArrow(my |length|), ¬
span(my isSpace)), xs)
script minimumIndent
on |λ|(a, tpl)
set n to fst(tpl)
bool(a, n, n < a and 0 < n)
end |λ|
end script
set indentUnit to foldl(minimumIndent, 100, tuples)
map(firstArrow(flipDiv(indentUnit)), tuples)
end indentLevelsFromLines


-- JSON SERIALISATIONS ------------------------------------

-- forestJSON :: [Tree a] -> JSON String
on forestJSON(trees)
toJSON(forestAsNestedPairs(trees))
end forestJSON

-- forestAsNestedPairs :: [Tree a] -> NestedPair [(a, [NestedPair])]
on forestAsNestedPairs(xs)
--A simple nested pair representation of a tree.
script go
on |λ|(tree)
{root of tree, map(go, nest of tree)}
end |λ|
end script
map(go, xs)
end forestAsNestedPairs

-- toJSON :: Show a => a -> String
on toJSON(a)
set blnAtom to {list, record} does not contain class of a
if blnAtom then
set obj to {a}
else
set obj to a
end if
set ca to current application
try
set {v, e} to ca's NSJSONSerialization's ¬
dataWithJSONObject:obj options:0 |error|:(reference)
on error
return ("(Not representatable as JSON)")
end try
set strJSON to ca's NSString's alloc()'s initWithData:v ¬
encoding:(ca's NSUTF8StringEncoding)
if blnAtom then
text 2 thru -2 of (strJSON as string)
else
strJSON as string
end if
end toJSON


-- GENERIC ------------------------------------------------

-- Node :: a -> [Tree a] -> Tree a
on Node(v, xs)
{type:"Node", root:v, nest:xs}
end Node


-- Tuple (,) :: a -> b -> (a, b)
on Tuple(a, b)
-- Constructor for a pair of values, possibly of two different types.
{type:"Tuple", |1|:a, |2|:b, length:2}
end Tuple


-- bool :: a -> a -> Bool -> a
on bool(f, t, p)
if p then
set v to t
else
set v to f
end if
-- Delayed evaluation, if needed.
if handler is class of v then
|λ|() of mReturn(v)
else
v
end if
end bool

-- compose (<<<) :: (b -> c) -> (a -> b) -> a -> c
on compose(f, g)
script
property mf : mReturn(f)
property mg : mReturn(g)
on |λ|(x)
mf's |λ|(mg's |λ|(x))
end |λ|
end script
end compose

-- concatMap :: (a -> [b]) -> [a] -> [b]
on concatMap(f, xs)
set lng to length of xs
set acc to {}
tell mReturn(f)
repeat with i from 1 to lng
set acc to acc & (|λ|(item i of xs, i, xs))
end repeat
end tell
return acc
end concatMap


-- flipDiv:: Int -> Int -> Int
on flipDiv(a)
-- Integer division, with arguments reversed
script
on |λ|(b)
b div a
end |λ|
end script
end flipDiv

-- Lift a simple function to one which applies to a tuple,
-- transforming only the first item of the tuple
-- firstArrow :: (a -> b) -> ((a, c) -> (b, c))
on firstArrow(f)
script
on |λ|(xy)
Tuple(mReturn(f)'s |λ|(|1| of xy), |2| of xy)
end |λ|
end script
end firstArrow

-- foldl :: (a -> b -> a) -> a -> [b] -> a
on foldl(f, startValue, xs)
tell mReturn(f)
set v to startValue
set lng to length of xs
repeat with i from 1 to lng
set v to |λ|(v, item i of xs, i, xs)
end repeat
return v
end tell
end foldl

-- fst :: (a, b) -> a
on fst(tpl)
if class of tpl is record then
|1| of tpl
else
item 1 of tpl
end if
end fst


-- intercalate :: String -> [String] -> String
on intercalate(delim, xs)
set {dlm, my text item delimiters} to ¬
{my text item delimiters, delim}
set str to xs as text
set my text item delimiters to dlm
str
end intercalate

-- isSpace :: Char -> Bool
on isSpace(c)
set i to id of c
32 = i or (9 ≤ i and 13 ≥ i)
end isSpace

-- length :: [a] -> Int
on |length|(xs)
set c to class of xs
if list is c or string is c then
length of xs
else
(2 ^ 29 - 1) -- (maxInt - simple proxy for non-finite)
end if
end |length|

-- listFromTuple :: (a, a ...) -> [a]
on listFromTuple(tpl)
items 2 thru -2 of (tpl as list)
end listFromTuple

-- lt :: Ord a => a -> a -> Bool
on lt(x)
script
on |λ|(y)
x < y
end |λ|
end script
end lt

-- map :: (a -> b) -> [a] -> [b]
on map(f, xs)
-- The list obtained by applying f
-- to each element of xs.
tell mReturn(f)
set lng to length of xs
set lst to {}
repeat with i from 1 to lng
set end of lst to |λ|(item i of xs, i, xs)
end repeat
return lst
end tell
end map

-- minimum :: Ord a => [a] -> a
on minimum(xs)
set lng to length of xs
if lng < 1 then return missing value
set m to item 1 of xs
repeat with x in xs
set v to contents of x
if v < m then set m to v
end repeat
return m
end minimum

-- mReturn :: First-class m => (a -> b) -> m (a -> b)
on mReturn(f)
-- 2nd class handler function lifted into 1st class script wrapper.
if script is class of f then
f
else
script
property |λ| : f
end script
end if
end mReturn

-- snd :: (a, b) -> b
on snd(tpl)
if class of tpl is record then
|2| of tpl
else
item 2 of tpl
end if
end snd

-- span :: (a -> Bool) -> [a] -> ([a], [a])
on span(f)
-- The longest (possibly empty) prefix of xs
-- that contains only elements satisfying p,
-- tupled with the remainder of xs.
-- span(p, xs) eq (takeWhile(p, xs), dropWhile(p, xs))
script
on |λ|(xs)
set lng to length of xs
set i to 0
tell mReturn(f)
repeat while i < lng and |λ|(item (i + 1) of xs)
set i to i + 1
end repeat
end tell
splitAt(i, xs)
end |λ|
end script
end span


-- splitAt :: Int -> [a] -> ([a], [a])
on splitAt(n, xs)
if n > 0 and n < length of xs then
if class of xs is text then
Tuple(items 1 thru n of xs as text, ¬
items (n + 1) thru -1 of xs as text)
else
Tuple(items 1 thru n of xs, items (n + 1) thru -1 of xs)
end if
else
if n < 1 then
Tuple({}, xs)
else
Tuple(xs, {})
end if
end if
end splitAt</lang>
{{Out}}
<pre>Outline:

The Rosetta stone
is a granodiorite stele
engraved
with Greek and Egyptian texts
in different scripts.
which, in the 19c, shed new light
on various homologies.

Forest from outline:

[["The Rosetta stone",[["is a granodiorite stele",[["engraved",[["with Greek and Egyptian texts",[]]]],["in different scripts.",[]]]],["which, in the 19c, shed new light",[["on various homologies.",[]]]]]]]

Nesting levels from forest:

[[0,"The Rosetta stone"],[1,"is a granodiorite stele"],[2,"engraved"],[3,"with Greek and Egyptian texts"],[2,"in different scripts."],[1,"which, in the 19c, shed new light"],[2,"on various homologies."]]

Forest rebuilt from nesting levels

[["The Rosetta stone",[["is a granodiorite stele",[["engraved",[["with Greek and Egyptian texts",[]]]],["in different scripts.",[]]]],["which, in the 19c, shed new light",[["on various homologies.",[]]]]]]]

Equality test:

(forestA = forestB) -> true</pre>


=={{header|Go}}==
=={{header|Go}}==
Line 535: Line 145:
</pre>
</pre>


=={{header|Haskell}}==
Using the rose tree constructor in the standard Data.Tree module.

Parses the initial tree from outline text, and writes out the flat
and nested structures in a JSON format:
<lang haskell>{-# LANGUAGE OverloadedStrings #-}

import qualified Data.Text.Lazy.Encoding as E
import qualified Data.Text.Lazy.IO as T
import qualified Data.Text.Lazy as T
import Control.Arrow (first)
import Data.Char (isSpace)
import Data.Bool (bool)
import Data.Tree
import Data.Aeson
import Data.Aeson.Text
import Control.Arrow ((***))

-- TREES <-> LIST OF LEVELS <-> TREES -----------------------
nestLevelsFromForest :: [Tree a] -> [(Int, a)]
nestLevelsFromForest xs =
let go level node =
(level, rootLabel node) : (subForest node >>= go (succ level))
in xs >>= go 0

forestFromNestLevels
:: Ord t
=> [(t, a)] -> Forest a
forestFromNestLevels pairs =
let go [] = []
go ((n, s):xs) =
uncurry (:) $ (Node s . go *** go) (span ((n <) . fst) xs)
in go pairs

-- INITIAL PARSE TREE OF OUTLINE --------------------------
nestLevelsFromLines xs =
let pairs = T.span isSpace <$> xs
indentUnit =
foldr
(\x a ->
let w = (T.length . fst) x
in bool a w (w < a && 0 < w))
maxBound
pairs
in first (flip div indentUnit . T.length) <$> pairs

-- DISPLAY OF JSON SERIALISATION --------------------------
showJSON
:: ToJSON a
=> a -> T.Text
showJSON = E.decodeUtf8 . encode . toJSON

-- TEST ---------------------------------------------------
forestA :: Forest T.Text
forestA = (forestFromNestLevels . nestLevelsFromLines) (T.lines outline)

nestLevels :: [(Int, T.Text)]
nestLevels = nestLevelsFromForest forestA

forestB :: [Tree T.Text]
forestB = forestFromNestLevels nestLevels

main :: IO ()
main = do
mapM_
T.putStrLn
[ "Initial parse tree from outline:\n"
, showJSON forestA
, "\nFlat list of nesting levels from parse tree:\n"
, showJSON nestLevels
, "\nTree rebuilt from nest levels:\n"
, showJSON forestB
]
putStrLn $
"\n\n(Reconstructed tree == parsed tree) -> " ++ show (forestA == forestB)

outline :: T.Text
outline =
"RosettaCode\n\
\ rocks\n\
\ code\n\
\ comparison\n\
\ wiki\n\
\ knocks\n\
\ golfing"</lang>
{{Out}}
<pre>Initial parse tree from outline:

[["RosettaCode",[["rocks",[["code",[]],["comparison",[]],["wiki",[]]]],["knocks",[["golfing",[]]]]]]]

Flat list of nesting levels from parse tree:

[[0,"RosettaCode"],[1,"rocks"],[2,"code"],[2,"comparison"],[2,"wiki"],[1,"knocks"],[2,"golfing"]]

Tree rebuilt from nest levels:

[["RosettaCode",[["rocks",[["code",[]],["comparison",[]],["wiki",[]]]],["knocks",[["golfing",[]]]]]]]


(Reconstructed tree == parsed tree) -> True</pre>

=={{header|JavaScript}}==
Parses the initial tree from outline text, and writes out the flat and nested structures in a minimal JSON format:
<lang javascript>(() => {
'use strict';

// main :: IO ()
const main = () => {

// (INDENT, STRING) PAIRS FROM OUTLINE ------------
const
indentLevelTuplesA = indentLevelsFromLines(
lines(strOutlineB)
);

// LIST OF TREES FROM LIST OF (INDENT, STRING) PAIRS
const
forestA = forestFromIndentLevels(
indentLevelTuplesA
);

// (INDENT, STRING) PAIRS FROM LIST OF TREES ------
const
indentLevelTuplesB = indentLevelsFromForest(forestA);

// LIST OF TREES FROM SECONDARY (INDENT, STRING) PAIRS
const forestB = forestFromIndentLevels(
indentLevelTuplesB
);

// JSON OUTPUT OF FORESTS AND INDENT TUPLES -------

console.log('Tree structure from outline:\n')
console.log(jsonFromForest(forestA));

console.log('\n\nIndent levels from tree structure:\n')
console.log(jsonFromIndentLevels(indentLevelTuplesB));

console.log('\nTree structure from indent levels:\n')
console.log(jsonFromForest(forestB));

console.log(
'(Reconstructed tree === parsed tree) -> ' +
Boolean(eq(forestA)(forestB))
);
};

// CONVERSIONS BETWEEN OUTLINES, TREES, AND (LEVEL, VALUE) PAIRS

// indentLevelsFromLines :: [String] -> [(Int, String)]
const indentLevelsFromLines = xs => {
const
indentTextPairs = xs.map(compose(
firstArrow(length), span(isSpace)
)),
indentUnit = minimum(indentTextPairs.flatMap(pair => {
const w = fst(pair);
return 0 < w ? [w] : [];
}));
return indentTextPairs.map(
firstArrow(flip(div)(indentUnit))
);
};

// forestFromIndentLevels :: [(Int, String)] -> [Tree String]
const forestFromIndentLevels = tuples => {
const go = xs =>
0 < xs.length ? (() => {
const [n, s] = Array.from(xs[0]);
return uncurry(cons)(
splitArrow(compose(Node(s), go))(go)(
span(compose(lt(n), fst))(
xs.slice(1)
)
)
);
})() : [];
return go(tuples);
};

// indentLevelsFromForest :: [Tree a] -> [(Int, a)]
const indentLevelsFromForest = trees => {
const go = n => node => [
[n, node.root]
]
.concat(node.nest.flatMap(go(1 + n)))
return trees.flatMap(go(0));
};

// JSON RENDERING OF NESTED LINES AND (LEVEL, VALUE) PAIRS

// jsonFromForest :: [Tree a] -> JSON String
const jsonFromForest = trees =>
JSON.stringify(
nestedListsFromForest(trees),
null, 2
);


// nestedListsFromForest :: [Tree a] -> NestedList a
const nestedListsFromForest = xs => {
const go = node => [node.root, node.nest.map(go)];
return xs.map(go);
};

// jsonFromIndentLevels :: [(Int, String)] -> JSON String
const jsonFromIndentLevels = xs =>
JSON.stringify(
xs.map(x => Array.from(x)),
null, 2
);


// GENERIC FUNCTIONS ----------------------------

// Node :: a -> [Tree a] -> Tree a
const Node = v => xs => ({
type: 'Node',
root: v, // any type of value (consistent across tree)
nest: xs || []
});

// Tuple (,) :: a -> b -> (a, b)
const Tuple = a => b => ({
type: 'Tuple',
'0': a,
'1': b,
length: 2
});

// compose (<<<) :: (b -> c) -> (a -> b) -> a -> c
const compose = (...fs) =>
x => fs.reduceRight((a, f) => f(a), x);

// cons :: a -> [a] -> [a]
const cons = x =>
xs => [x].concat(xs)

// div :: Int -> Int -> Int
const div = x => y => Math.floor(x / y);

// eq (==) :: Eq a => a -> a -> Bool
const eq = a => b => {
const t = typeof a;
return t !== typeof b ? (
false
) : 'object' !== t ? (
'function' !== t ? (
a === b
) : a.toString() === b.toString()
) : (() => {
const kvs = Object.entries(a);
return kvs.length !== Object.keys(b).length ? (
false
) : kvs.every(([k, v]) => eq(v)(b[k]));
})();
};

// firstArrow :: (a -> b) -> ((a, c) -> (b, c))
const firstArrow = f => xy => Tuple(f(xy[0]))(
xy[1]
);

// flip :: (a -> b -> c) -> b -> a -> c
const flip = f =>
1 < f.length ? (
(a, b) => f(b, a)
) : (x => y => f(y)(x));

// foldl1 :: (a -> a -> a) -> [a] -> a
const foldl1 = f => xs =>
1 < xs.length ? xs.slice(1)
.reduce(uncurry(f), xs[0]) : xs[0];

// fst :: (a, b) -> a
const fst = tpl => tpl[0];

// isSpace :: Char -> Bool
const isSpace = c => /\s/.test(c);

// Returns Infinity over objects without finite length.
// This enables zip and zipWith to choose the shorter
// argument when one is non-finite, like cycle, repeat etc

// length :: [a] -> Int
const length = xs =>
(Array.isArray(xs) || 'string' === typeof xs) ? (
xs.length
) : Infinity;

// lines :: String -> [String]
const lines = s => s.split(/[\r\n]/);

// lt (<) :: Ord a => a -> a -> Bool
const lt = a => b => a < b;

// minimum :: Ord a => [a] -> a
const minimum = xs =>
0 < xs.length ? (
foldl1(a => x => x < a ? x : a)(xs)
) : undefined;

// showLog :: a -> IO ()
const showLog = (...args) =>
console.log(
args
.map(JSON.stringify)
.join(' -> ')
);

// span :: (a -> Bool) -> [a] -> ([a], [a])
const span = p => xs => {
const iLast = xs.length - 1;
return splitAt(
until(i => iLast < i || !p(xs[i]))(
succ
)(0)
)(xs);
};

// Compose a function (from a tuple to a tuple),
// (with separate transformations for fst and snd)

// splitArrow (***) :: (a -> b) -> (c -> d) -> ((a, c) -> (b, d))
const splitArrow = f => g =>
tpl => Tuple(f(tpl[0]))(
g(tpl[1])
);

// splitAt :: Int -> [a] -> ([a], [a])
const splitAt = n => xs =>
Tuple(xs.slice(0, n))(
xs.slice(n)
);

// succ :: Enum a => a -> a
const succ = x => 1 + x;

// uncurry :: (a -> b -> c) -> ((a, b) -> c)
const uncurry = f =>
function() {
const
args = Array.from(arguments),
a = 1 < args.length ? (
args
) : args[0];
return f(a[0])(a[1]);
};

// until :: (a -> Bool) -> (a -> a) -> a -> a
const until = p => f => x => {
let v = x;
while (!p(v)) v = f(v);
return v;
};

// SAMPLE OUTLINES ------------------------------------

const strOutlineA = `Heilmeier catechism
Objectives and benefits
What are you trying to do?
Articulate your objectives using absolutely no jargon.
What are the problems you address ?
How is it done today,
and what are the limits of current practice?
What is your solution ?
What is new in your approach
and why do you think it will be successful?
Who cares? If you are successful, what difference will it make?
Costs
What are the risks?
How much will it cost?
How long will it take?
Indicators
What are the mid-term and final “exams” to check for success?`;

const strOutlineB = `Rosetta stone
is a granodiorite stele
engraved
with Greek and Egyptian texts
in different scripts.
which shed new light
on various homologies.`;

// MAIN ---
return main();
})();</lang>
{{Out}}
<pre>Tree structure from outline:

[
[
"Rosetta stone",
[
[
"is a granodiorite stele",
[
[
"engraved",
[
[
"with Greek and Egyptian texts",
[]
]
]
],
[
"in different scripts.",
[]
]
]
],
[
"which shed new light",
[
[
"on various homologies.",
[]
]
]
]
]
]
]

Indent levels from tree structure:

[
[
0,
"Rosetta stone"
],
[
1,
"is a granodiorite stele"
],
[
2,
"engraved"
],
[
3,
"with Greek and Egyptian texts"
],
[
2,
"in different scripts."
],
[
1,
"which shed new light"
],
[
2,
"on various homologies."
]
]

Tree structure from indent levels:

[
[
"Rosetta stone",
[
[
"is a granodiorite stele",
[
[
"engraved",
[
[
"with Greek and Egyptian texts",
[]
]
]
],
[
"in different scripts.",
[]
]
]
],
[
"which shed new light",
[
[
"on various homologies.",
[]
]
]
]
]
]
]
(Reconstructed tree === parsed tree) -> true</pre>


=={{header|Python}}==
=={{header|Python}}==
===Procedural===
Just arranges the standard lists and tuples for the datastructures allowing pprint to show the different arrangement of storage.
Just arranges the standard lists and tuples for the datastructures allowing pprint to show the different arrangement of storage.


Line 1,106: Line 219:
('mocks',
('mocks',
[('trolling', [])])])</pre>
[('trolling', [])])])</pre>

===Functional===

Using a Node constructor with '''root''' and '''nest''' keys for the value and sub-forest of each tree node, and serialising both trees and nesting-level lists to JSON-compatible formats.

Functional composition, as an alternative to '''.append()''' and '''.pop()''' mutations.

(Initial tree constructed as the parse of an outline text)

{{Works with|Python|3.7}}
<lang python>'''Tree data structures'''

from itertools import chain, takewhile
import json


# Node :: a -> [Tree a] -> Tree a
def Node(v):
'''Constructor for a Tree node which connects a
value of some kind to a list of zero or
more child trees.
'''
return lambda xs: {'type': 'Tree', 'root': v, 'nest': xs}


# forestFromNestLevels :: [(Int, a)] -> [Tree a]
def forestFromNestLevels(tuples):
'''A list of trees derived from a list of values paired
with integers giving their levels of indentation.
'''
def go(xs):
if xs:
(intIndent, v) = xs[0]
(firstTreeLines, rest) = span(
lambda x: intIndent < x[0]
)(xs[1:])
return [Node(v)(go(firstTreeLines))] + go(rest)
else:
return []
return go(tuples)


# nestLevelsFromForest :: [Tree a] -> [(Int, a)]
def nestLevelsFromForest(xs):
'''A flat list of (nest level, value) tuples,
representing a series of trees.
'''
def go(level):
return lambda node: [(level, node['root'])] + concatMap(
go(1 + level)
)(node['nest'])
return concatMap(go(0))(xs)


# TEST ----------------------------------------------------
# main :: IO ()
def main():
'''Conversion from trees to flat lists of nest levels,
and back again, with each stage shown as a JSON
string.
'''
forestA = forestFromNestLevels(
indentLevelsFromLines(OUTLINE.splitlines())
)
nestLevels = nestLevelsFromForest(forestA)
forestB = forestFromNestLevels(nestLevels)

for x in [
'Parse tree from outline text:\n',
forestJSON(forestA),

'\nNesting level list from tree:\n',
json.dumps(nestLevels, indent=2),

'\nTree rebuilt from nesting level list:\n',
forestJSON(forestB),
]:
print(x)
print(
'(Reconstructed forest == parsed forest) -> ' +
str(forestA == forestB)
)


# INITIAL TREE FROM PARSE OF OUTLINE TEXT -----------------

# indentLevelsFromLines :: [String] -> [(Int, String)]
def indentLevelsFromLines(xs):
'''Each input line stripped of leading
white space, and tupled with a preceding integer
giving its level of indentation from 0 upwards.
'''
indentTextPairs = [
(n, s[n:]) for (n, s)
in ((len(list(takewhile(isSpace, x))), x) for x in xs)
]
indentUnit = min(concatMap(
lambda x: [x[0]] if x[0] else []
)(indentTextPairs))
return [
(x[0] // indentUnit, x[1])
for x in indentTextPairs
]


# JSON SERIALISATION --------------------------------------

# forestJSON :: [Tree a] -> JSON String
def forestJSON(trees):
'''A simple JSON serialisation of a list of trees, with
each tree node represented as a [value, nodes] pair.
'''
return json.dumps(
forestAsNestedPairs(trees),
indent=2
)


# forestAsNestedPairs :: [Tree a] -> NestedPair [(a, [NestedPair])]
def forestAsNestedPairs(xs):
'''A simple nested pair representation of a tree.'''
def go(node):
return [node['root'], [go(x) for x in node['nest']]]
return [go(x) for x in xs]


# GENERIC -------------------------------------------------

# concatMap :: (a -> [b]) -> [a] -> [b]
def concatMap(f):
'''A concatenated list or string over which a function f
has been mapped.
The list monad can be derived by using an (a -> [b])
function which wraps its output in a list (using an
empty list to represent computational failure).
'''
return lambda xs: (''.join if isinstance(xs, str) else list)(
chain.from_iterable(map(f, xs))
)


# isSpace :: Char -> Bool
# isSpace :: String -> Bool
def isSpace(s):
'''True if s is not empty, and
contains only white space.
'''
return s.isspace()


# span :: (a -> Bool) -> [a] -> ([a], [a])
def span(p):
'''The longest (possibly empty) prefix of xs
that contains only elements satisfying p,
tupled with the remainder of xs.
span p xs is equivalent to (takeWhile p xs, dropWhile p xs).
'''
def go(xs):
prefix = list(takewhile(p, xs))
return (prefix, xs[len(prefix):])
return lambda xs: go(xs)


# MAIN ---
if __name__ == '__main__':
OUTLINE = '''Rosetta stone
is a granodiorite stele
engraved
with Greek and Egyptian texts
in different scripts.
which shed new light
on various homologies.'''

main()</lang>
{{Out}}
<pre>Parse tree from outline text:

[
[
"Rosetta stone",
[
[
"is a granodiorite stele",
[
[
"engraved",
[
[
"with Greek and Egyptian texts",
[]
]
]
],
[
"in different scripts.",
[]
]
]
],
[
"which shed new light",
[
[
"on various homologies.",
[]
]
]
]
]
]
]

Nesting level list from tree:

[
[
0,
"Rosetta stone"
],
[
1,
"is a granodiorite stele"
],
[
2,
"engraved"
],
[
3,
"with Greek and Egyptian texts"
],
[
2,
"in different scripts."
],
[
1,
"which shed new light"
],
[
2,
"on various homologies."
]
]

Tree rebuilt from nesting level list:

[
[
"Rosetta stone",
[
[
"is a granodiorite stele",
[
[
"engraved",
[
[
"with Greek and Egyptian texts",
[]
]
]
],
[
"in different scripts.",
[]
]
]
],
[
"which shed new light",
[
[
"on various homologies.",
[]
]
]
]
]
]
]
(Reconstructed forest == parsed forest) -> True</pre>

Revision as of 08:42, 18 October 2019

Tree datastructures is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

The following shows a tree of data with nesting denoted by visual levels of indentation: 

RosettaCode
    rocks
        code
        comparison
        wiki
    mocks
        trolling

A common datastructure for trees is to define node structures having a name and a, (possibly empty), list of child nodes. The nesting of nodes captures the indentation of the tree. Lets call this the nest form. 

# E.g. if child nodes are surrounded by brackets
#      and separated by commas then:
RosettaCode(rocks(code, ...), ...)
# But only an _example_

Another datastructure for trees is to construct from the root an ordered list of the nodes level of indentation and the name of that node. The indentation for the root node is zero; node 'rocks is indented by one level from the left, and so on. Lets call this the indent form. 

0 RosettaCode
1 rocks
2 code
...
Task
  1. Create/use a nest datastructure format and textual representation for arbitrary trees.
  2. Create/use an indent datastructure format and textual representation for arbitrary trees.
  3. Create methods/classes/proceedures/routines etc to:
    1. Change from a nest tree datastructure to an indent one.
    2. Change from an indent tree datastructure to a nest one
  4. Use the above to encode the example at the start into the nest format, and show it.
  5. transform the initial nest format to indent format and show it.
  6. transform the indent format to final nest format and show it.
  7. Compare initial and final nest formats which should be the same.
Note
  • It's all about showing aspects of the contrasting datastructures as they hold the tree.
  • Comparing nested datastructures is secondary - saving formatted output as a string then a string compare would suffice for this task, if its easier.
  • The word "trolling" is substituted for the original, less appropriate, "golfing" in the tree above as golfing can be friendly fun! (just not for RC examples). Please update language examples appropriately.


Show all output on this page.

Go

<lang go>package main

import ( 

   "fmt"
   "strings"

)

type nNode struct { 

   name     string
   children []nNode

}

type iNode struct { 

   level int
   name  string

}

func printNest(n nNode, level int) { 

   if level == 0 {
       fmt.Println("\n==Nest form==\n")
   }
   fmt.Printf("%s%s\n", strings.Repeat("  ", level), n.name)
   for _, c := range n.children {
       fmt.Printf("%s", strings.Repeat("  ", level+1))
       printNest(c, level+1)
   }

}

func toNest(iNodes []iNode, start, level int, n *nNode) { 

   if level == 0 {
       n.name = iNodes[0].name
   }
   for i := start + 1; i < len(iNodes); i++ {
       if iNodes[i].level == level+1 {
           c := nNode{iNodes[i].name, nil}
           toNest(iNodes, i, level+1, &c)
           n.children = append(n.children, c)
       } else if iNodes[i].level <= level {
           return
       }
   }

}

func printIndent(iNodes []iNode) { 

   fmt.Println("\n==Indent form==\n")
   for _, n := range iNodes {
       fmt.Printf("%d %s\n", n.level, n.name)
   }

}

func toIndent(n nNode, level int, iNodes *[]iNode) { 

   *iNodes = append(*iNodes, iNode{level, n.name})
   for _, c := range n.children {
       toIndent(c, level+1, iNodes)
   }

}

func main() { 

   n1 := nNode{"RosettaCode", nil}
   n2 := nNode{"rocks", []nNode{{"code", nil}, {"comparison", nil}, {"wiki", nil}}}
   n3 := nNode{"mocks", []nNodeTemplate:"golfing", nil}
   n1.children = append(n1.children, n2, n3)
   printNest(n1, 0)
   var iNodes []iNode
   toIndent(n1, 0, &iNodes)
   printIndent(iNodes)
   var n nNode
   toNest(iNodes, 0, 0, &n)
   printNest(n, 0)

}</lang>

Output:
==Nest form==

RosettaCode
    rocks
        code
        comparison
        wiki
    mocks
        golfing

==Indent form==

0 RosettaCode
1 rocks
2 code
2 comparison
2 wiki
1 mocks
2 golfing

==Nest form==

RosettaCode
    rocks
        code
        comparison
        wiki
    mocks
        golfing


Python

Just arranges the standard lists and tuples for the datastructures allowing pprint to show the different arrangement of storage.

<lang python>from pprint import pprint as pp

def to_indent(node, depth=0, flat=None): 

   if flat is None:
       flat = []
   if node:
       flat.append((depth, node[0]))
   for child in node[1]:
       to_indent(child, depth + 1, flat)
   return flat

def to_nest(lst, depth=0, level=None): 

   if level is None:
       level = []
   while lst:
       d, name = lst[0]
       if d == depth:
           children = []
           level.append((name, children))
           lst.pop(0)
       elif d > depth:  # down
           to_nest(lst, d, children)
       elif d < depth:  # up
           return
   return level[0] if level else None

if __name__ == '__main__': 

   print('Start Nest format:')
   nest = ('RosettaCode', [('rocks', [('code', []), ('comparison', []), ('wiki', [])]), 
                           ('mocks', [('trolling', [])])])
   pp(nest, width=25)

   print('\n... To Indent format:')
   as_ind = to_indent(nest)
   pp(as_ind, width=25)

   print('\n... To Nest format:')
   as_nest = to_nest(as_ind)
   pp(as_nest, width=25)

   if nest != as_nest:
       print("Whoops round-trip issues")</lang>
Output:
Start Nest format:
('RosettaCode',
 [('rocks',
   [('code', []),
    ('comparison', []),
    ('wiki', [])]),
  ('mocks',
   [('trolling', [])])])

... To Indent format:
[(0, 'RosettaCode'),
 (1, 'rocks'),
 (2, 'code'),
 (2, 'comparison'),
 (2, 'wiki'),
 (1, 'mocks'),
 (2, 'trolling')]

... To Nest format:
('RosettaCode',
 [('rocks',
   [('code', []),
    ('comparison', []),
    ('wiki', [])]),
  ('mocks',
   [('trolling', [])])])
Retrieved from "https://rosettacode.org/wiki/Tree_datastructures?oldid=294507"