CODEWITHSUNDEEP
javascriptmultidimensional-arrayaverage
Josiah
Josiah

Reputation: 654

Calculating overall average of multidimensional array in JavaScript

How would I go about calculating the average of all the values in a multidimensional array? I've written a function to calculate the average from a 1-dimensional array, but I'm not sure what the best method is when there are more than 1-dimensions.

For example, let's say we have the following:

var A = Array(3);
for (i=0; i<A.length; i++) {
    A[i] = new Array(2);
    for (j=0; j<A[i].length; j++) {
        A[i][j] = i+j;
    }
}

Therefore, A is a 2-dimensional array, or 3x2 matrix:

A = 0   1
    1   2
    2   3

So I'd like to find the average of all the values, which in this case would equal 1.5. I imagine I need to create a new 1-dimensional array of all the values, which I could then feed into my averaging function. However, I'm not sure of the easiest way to do this when the array is highly-dimensional (e.g. 5x3x6x9).

Thanks!

EDIT

Thanks everyone! I've used your advice and flattened the array using code I found in one of the attached links which uses the reduce function. My averaging function is now like this:

function average(x) {

    // Flatten multi-dimensional array
    while (x[0] instanceof Array) {
        x = x.reduce( function(a, b) { return a.concat(b); } );
    }

    // Calculate average
    return x.reduce( function(a, b) { return a + b; } )/x.length;
}

Upvotes: 0

Views: 4515

Answers (4)

Jord&#227;o
Jord&#227;o

Reputation: 56457

You can flatten your multidimensional-array with this function:

function flatten(arr) {
    var acc = [];
    var f = function(arr) {
        for (var i = 0; i < arr.length; ++i) {
            if (arr[i] instanceof Array) {
                f(arr[i]);
            }
            else {
                acc.push(arr[i]);
            }
        }
    };
    f(arr);
    return acc;
}

And then you can calculate the average with your function.

Upvotes: 1

kennebec
kennebec

Reputation: 104760

// The simplest method is to flatten the array

Array.prototype.flatten= function(){
var A= [];
this.forEach(function(itm){
    if(!itm || !itm.flatten)A.push(itm);
    else{
        A= A.concat(itm.flatten());
    }
});
return A;
}
// shim for older browsers (without array forEach)
Array.prototype.forEach= [].forEach || function(fun, scope){
    var T= this, L= T.length, i= 0;
    if(typeof fun== 'function'){
        while(i< L){
            if(i in T){
                fun.call(scope, T[i], i, T);
            }
            ++i;
        }
    }
    return T;
}

var a=[[1,2,3,[1,2,3]],[4,5,6,[7,8,[1,2,3,[1,2]]]],11,[1,[2,[2,4,[5]]]]];
a.flatten().join('\n')

/*  returned value: (String)
1
2
3
1
2
3
4
5
6
7
8
1
2
3
1
2
11
1
2
2
4
5
*/

Upvotes: 1

T.J. Crowder
T.J. Crowder

Reputation: 1073968

I don't see any particular reason you need to create a new array. Just loop through the ones you have:

var i, j, sub, total, count, avg;

total = count = 0;
for (i = 0; i < A.length; ++i) {
    sub = A[i];
    count += sub.length;
    for (j = 0; j < sub.length; ++j) {
        total += sub[j];
    }
}
avg = count === 0 ? NaN : total / count;

Note that the above assumes the arrays are not sparse (they aren't in your example).

Upvotes: 1

Benjie
Benjie

Reputation: 7946

You can use this code to flatten the multi-dimensional array:

function flatten(array){
    var flat = [];
    for (var i = 0, l = array.length; i < l; i++){
        var type = Object.prototype.toString.call(array[i]).split(' ').pop().split(']').shift().toLowerCase();
        if (type) { flat = flat.concat(/^(array|collection|arguments|object)$/.test(type) ? flatten(array[i]) : array[i]); }
    }
    return flat;
}

and then just sum and divide:

var total = 0;
for (var i = 0, l = flattenedArray.length; i<l; i++) {
  total += flattenedArray[i];
}
var average = total/flattenedArray.length;

Upvotes: 1

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