Question

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 3×2 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;
}

Answer 1

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;