Averages/Arithmetic mean
Write a program to find the mean (arithmetic average) of a numeric vector. The program should work on a zero-length vector (with an answer of 0).
You are encouraged to solve this task according to the task description, using any language you may know.
Ada
This example shows how to pass a zero length vector as well as a larger vector.
with Ada.Float_Text_Io; use Ada.Float_Text_Io; with Ada.Text_IO; use Ada.Text_IO; procedure Mean_Main is type Vector is array(Positive range <>) of Float; function Mean(Item : Vector) return Float is Sum : Float := 0.0; Result : Float := 0.0; begin for I in Item'range loop Sum := Sum + Item(I); end loop; if Item'Length > 0 then Result := Sum / Float(Item'Length); end if; return Result; end Mean; A : Vector := (3.0, 1.0, 4.0, 1.0, 5.0, 9.0); begin Put(Item => Mean(A), Fore => 1, Exp => 0); New_Line; -- test for zero length vector Put(Item => Mean(A(1..0)), Fore => 1, Exp => 0); New_Line; end Mean_Main;
Output:
3.83333 0.00000
BASIC
Assume the numbers are in a DIM named nums.
mean = 0 sum = 0; FOR i = LBOUND(nums) TO UBOUND(nums) sum = sum + nums(i); NEXT i size = UBOUND(nums) - LBOUND(nums) + 1 PRINT "The mean is: "; IF size <> 0 THEN PRINT (sum / size) ELSE PRINT 0 END IF
C++
double mean(std::vector<double> const& vNumbers) { double sum = 0; for( std::vector<double>::iterator i = vNumbers.begin(); vNumbers.end() != i; ++i ) sum += *i; if( 0 == vNumbers.size() ) return 0; else return sum / vNumbers.size(); }
Shorter (and more idiomatic) version:
#include <vector> #include <algorithm> double mean(std::vector<double> const& numbers) { if (numbers.empty()) return 0; return std::accumulate(numbers.begin(), numbers.end(), 0.0) / numbers.size(); }
Common Lisp
(defun mean (sequence) (let ((length (length sequence))) (if (zerop length) 0 (/ (reduce #'+ sequence) length))))
D
Using template to make the mean function work for higher-rank array.
module mean ; import std.stdio ; real mean(T)(T[] a) { static if(is(T U : U[])) { // recursively unfold the multi-array T u ; foreach(e ; a) u ~= e ; return u.mean() ; } else { // do the math if(a.length == 0) return 0.0 ; real sum = 0.0 ; foreach(e ; a) sum += e ; return sum / a.length ; } } void main() { int[] array = [3,1,4,1,5,9]; real[][][] multi = [[[1,2,2],[2,3,4],[4,5,7]], [[4,1,3],[0,3,1],[4,4,6]], [[1,3,3],[2,7,8],[9,1,5]]] ; writefln("array : ", array.mean()) ; writefln("multi : ", multi.mean()) ; }
Forth
: fmean ( addr n -- f ) 0e dup 0= if 2drop exit then tuck floats bounds do i f@ f+ 1 floats +loop 0 d>f f/ ; create test 3e f, 1e f, 4e f, 1e f, 5e f, 9e f, test 6 fmean f. \ 3.83333333333333
Haskell
mean xs = sum xs / Data.List.genericLength xs
IDL
If truly only the mean is wanted, one could use
x = [3,1,4,1,5,9] print,mean(x)
But mean() is just a thin wrapper returning the zeroth element of moment() :
print,moment(x) ; ==> 3.83333 8.96667 0.580037 -1.25081
which are mean, variance, skewness and kurtosis.
There are no zero-length vectors in IDL. Every variable has at least one value or otherwise it is <Undefined>.
J
mean=: +/ % #
That is, sum divided by the number of items. The verb also works on higher-ranked arrays. For example:
mean 3 1 4 1 5 9 3.83333 mean $0 NB. $0 is a zero-length vector 0 x=: 20 4 ?@$ 0 NB. a 20-by-4 table of random (0,1) numbers mean x 0.58243 0.402948 0.477066 0.511155
The computation can also be written as a loop. It is shown here for comparison only and is highly non-preferred compared to the version above.
mean1=: 3 : 0 z=. 0 for_i. i.#y do. z=. z+i{y end. z % #y ) mean1 3 1 4 1 5 9 3.83333 mean1 $0 0 mean1 x 0.58243 0.402948 0.477066 0.511155
Java
Assume the numbers are in a double array called "nums".
... double mean = 0; double sum = 0; for(double i : nums){ sum += i; } System.out.println("The mean is: " + ((nums.length != 0) ? (sum / nums.length) : 0)); ...
JavaScript
function mean(array) { var sum = 0; for(var i in array) sum += array[i]; return array.length ? sum / array.length : 0; } alert( mean( [1,2,3,4,5] ) ); // 3
MAXScript
fn mean data = ( total = 0 for i in data do ( total += i ) if data.count == 0 then 0 else total as float/data.count ) print (mean #(3, 1, 4, 1, 5, 9))
OCaml
These functions return a float:
let mean_floats xs = if xs = [] then 0. else List.fold_left (+.) 0. xs /. float_of_int (List.length xs)
let mean_ints xs = mean_floats (List.map float_of_int xs)
Perl
sub avg(@_) { $count = 0; $sum = 0; foreach (@_) { $sum += $_; $count++; } return $count > 0 ? $sum / $count : 0; } print avg(qw(3 1 4 1 5 9))."\n";
Output:
3.83333333333333
With module Data::Average. (For zero-length array returns ().)
use Data::Average; my $d = Data::Average->new; $d->add($_) foreach (qw(3 1 4 1 5 9)); print $d->avg."\n"
Output:
3.83333333333333
Python
def avg(data): return sum(data)/float(len(data)) if len(data)!=0 else 0 print avg([3,1,4,1,5,9])
Output:
3.83333333333333
def avg(data): if len(data)==0: return 0 else: return sum(data)/float(len(data)) print avg([3,1,4,1,5,9])
Output:
3.83333333333333
Scheme
(define (mean l) (if (null? l) 0 (/ (apply + l) (length l))))
> (mean (list 3 1 4 1 5 9)) 3 5/6