How to add array of arrays in javascript

Question

I have a Javascript array with multiple arrays inside. I was trying to loop through the array to return an aggregated array. So far I have done following with no luck:

var a = [[1,2,3],[4,5,56],[2,5,7]];
var x = [];
for ( var i = 0; i < a.length; i++) {
 for ( var j = 0; j < a[i].length; j++) {
 console.log(a[i][i] = a[i][j]+a[j][i]);
 }
}

I am trying to obtain the following result:

console.log(a); // -> [7,12,66]

Any suggestions or pin points where I can look for examples of similar things would be appreciated.

Answer 1

assuming the elements of a has the same length, the following should work

var x=[];
for(var i=0; i<a[0].length; i++){
 var s = 0; 
 for(var j=0; j<a.length; j++){
 s += a[j][i];
 }
 x.push(s);
}

Answer 2

a[0].map(function(b,i){return a.reduce(function(c,d){return c+d[i];},0);})
// [7, 12, 66]

Answer 3

From dc2 to dc1, try this:

var a = [[1,2,3],[4,5,56],[2,5,7]];
var x = [];
for ( var i =0; i < a.length; i++){
 for ( var j = 0; j < a[i].length; j++){
 x[j] = x[j] || 0;
 x[j] = x[j] + a[i][j];
 }
}

This worked in testing, and doesn't error with different array lengths.