Swap rows with columns (transposition) of a matrix in javascript

Question

For instance I have a matrix like this:

|1 2 3|    
|4 5 6|
|7 8 9|

and I need it to convert into a matrix like this:

|1 4 7|    
|2 5 8|
|3 6 9|

What is the best and optimal way to achieve this goal?

Answer 1

DuckDucking turned up this by Ken. Surprisingly, it's even more concise and complete than Nikita's answer. It retrieves column and row lengths implicitly within the guts of map().

function transpose(a) {
    return Object.keys(a[0]).map(function(c) {
        return a.map(function(r) { return r[c]; });
    });
}

console.log(transpose([
    [1,2,3],
    [4,5,6],
    [7,8,9]
]));