Unflatten Arrays into groups of fours [closed]

Question

I have an array that is as follows:

var someArray = ['val1','val2','val3','val4','val5','val6','val7','val8','val9','val10','val11','val12'];

I'm trying to figure out some elegant way, using underscore, of simply converting it to an array of arrays like so...

[['val1','val2','val3','val4'], ['val5','val6','val7','val8'], ['val9','val10','val11','val12']]

Where each index of the new array is groups of four elements from the first array. Is there an easy elegant way of doing this with underscore.js.

Answer 1

Underscore, since you asked: (Example)

var i = 4, list = _.groupBy(someArray, function(a, b){
    return Math.floor(b/i);
});
newArray = _.toArray(list);

Vanilla JS: (Example)

var newArray = [], size = 4;
while (someArray.length > 0) newArray.push(someArray.splice(0, size));

Answer 2

Pure JavaScript solution, using splice():

Object.defineProperty( Array.prototype, 'eachConsecutive', {
  value:function(n){
    var copy = this.concat(), result = [];
    while (copy.length) result.push( copy.splice(0,n) );
    return result;        
  }
});

var someArray = ['val1','val2','val3','val4','val5','val6','val7','val8','val9','val10','val11','val12'];
var chunked = someArray.eachConsecutive(4);
//-> [["val1","val2","val3","val4"],["val5","val6","val7","val8"],["val9","val10","val11","val12"]]