Convert array within array to averages

Question

I am trying to convert:

var ic = [[[123,231,12],[56,43,124]],[[78,152,76],[64,132,200]]]

to (each element of the sub array has the average value of the sub array)

var ig = [[[122,122,122],[74,74,74]],[[102,102,102],[132,132,132]]]

Here is my code, the average function works, but it is not returning the correct new array:

var color2grey = function (image /* this is the image in color*/) {

const average = function([a,b,c]) {
return [((a+b+c)/3), ((a+b+c)/3), ((a+b+c)/3)]
};

return image.map(function(subArray) {
 average(subArray);
});

}

This is what I am getting:

returns- (2) [undefined, undefined] 0 : undefined 1 : undefined length : 2 proto : Array(0)

You could try adding the output you are getting, what the function returns so it helps in debugging. — Stuti Rastogi
– Stuti Rastogi, Commented May 16, 2017 at 13:04
returns- (2) [undefined, undefined] 0 : undefined 1 : undefined length : 2 proto : Array(0) — MaxES
– MaxES, Commented May 16, 2017 at 13:06

Nenad Vracar · Accepted Answer · 2017-05-16 13:10:12Z

1

You can use map() method to make new array and inside you can use reduce() to calculate average of each array and Array.fill() to add avg values to new array.

var ic = [[[123,231,12],[56,43,124]],[[78,152,76],[64,132,200]]] 

var result = ic.map(a => a.map(function(e) {
  var avg = e.reduce((r, e) => r + e) / e.length
  return Array(e.length).fill(parseInt(avg))
}))

console.log(result)

answered May 16, 2017 at 13:10

Nenad Vracar

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Comments

Nina Scholz · Accepted Answer · 2017-05-16 13:25:19Z

You could map the outer arrays, get the average of the most inner array and map for each item the average value.

var ic = [[[123, 231, 12], [56, 43, 124]], [[78, 152, 76], [64, 132, 200]]],
    ig = ic.map(function (a) {
        return a.map(function (b) {
            var avg = Math.floor(b.reduce(function (a, b) { return a + b; }) / b.length);
            return b.map(function () { return avg; });
        });
    });

console.log(ig);

.as-console-wrapper { max-height: 100% !important; top: 0; }

ES6

var avg = array => array.reduce((a, b) => a + b) / array.length,
    ic = [[[123, 231, 12], [56, 43, 124]], [[78, 152, 76], [64, 132, 200]]],
    ig = ic.map(a => a.map(b => Array(b.length).fill(Math.floor(avg(b)))));

console.log(ig);

.as-console-wrapper { max-height: 100% !important; top: 0; }

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