Sum array of arrays (matrix) vertically efficiently/elegantly

Question

In Javascript, if I have an array of arrays representing a matrix, say

x = [
    [1,2,3,4],
    [5,6,7,8],
    [9,10,11,12]
];

summing it

Answer 1

Really elegant only for square matrix from me.

   x = [[1,2,3,4],
        [5,6,7,8],
        [9,10,11,12]
    ];
    var sum = function(arr) {
      return arr.reduce(function(a, b){ return a + b; }, 0);
    };

    x.map(function(row, i) {
      return sum(x.map(function(row) { return row[i]; }));
    });

http://jsfiddle.net/btux9s2d/ example with console log.

for any size matrix, not so elegant, but maybe will help you on your way: http://jsfiddle.net/btux9s2d/2/