Get a 1-dimension array of random elements from a 2-dimensions array

window.random = function(rows, nbToReturn) {
    // group all sub arrays in a flat array
    return [].concat.apply([], rows)
        // randomize
        .sort(function(){return 0.5 - Math.random()})
        // takes the nbToReturn first
        .splice(0, nbToReturn);
};

Use:

var a = [[1,2,3],[4,5,6],[7,8,9]];
console.log(random(a, 4));

displays:

[4, 5, 6, 1]

Link to gist: https://gist.github.com/padawin/4b40456e48591dea5aeb