Underscore functional javascript

Question

I'm trying to switch in general to functional programming and want to use underscore for JavaScript.

But I'm stuck at first base. I could not create an array at all and resorted to imperative language, and I can't seem to transform them properly either: n.length is correct, but n[0].length is undefined (see fiddle)

var a = new Array(5);
for (i = 0; i < a.length; i++) {
    a[i] = new Array(6);
}
var n = _.map(a, function (row, rowIdx) {
    _.map(row, function(col, colIdx) {
        return rowIdx * colIdx
    });
});

console.log(a.length)
console.log(n.length)
console.log(a[0].length);
console.log(n[0].length);

Answer 1

To "functionally" create a 5 x 6 matrix using underscore, you could do something like this:

var matrix = _.range(5).map(function (i) {
    return _.range(6).map(function (j) {
        return j * i;
    });
});

The _.range function (documentation) is a shorthand for creating arrays that are filled with sequential numbers. For example, _.range(5) returns the array [0,1,2,3,4]. Ranges start at zero.

If you didn't want to use _.range, you could do this with raw JavaScript by using array literals:

var matrix = [0,1,2,3,4].map(function (i) {
    return [0,1,2,3,4,5].map(function (j) {
        return j * i;
    });
});

Answer 2

Another way to create a matrix would be to use _.times:

var matrix = _.times(6, function(x){
    return _.times(7, function(y){

        // do whatever needs to be done to calculate the value at x,y

        return x + ',' + y;
    });
});