One dimensional to two dimensional array javascript

Question

First I have an array like:

arr = [[r,g,b,a],[r,g,b,a],[r,g,b,a],[r,g,b,a],[r,g,b,a],[r,g,b,a]]

I can 'flatten' it using

arr = Array.prototype.concat.apply([],arr)

or using a for-next loop and push.apply

Then I got:

[r,g,b,a,r,g,b,a,r,g,b,a,r,g,b,a,r,g,b,a]

How do I get it back to its original format as easy as possible?

• Jonas Elfström: Just for fun in JavaScript 1.6 (maybe jQuery) arr.join().match(/\d+,\d+,\d+,\d+/g).map(function(s) { return s.split(",") } )
• Blaise: Isn't it a possibility to work with one format? Saves a lot of looping.

Answer 1

Something like this, perhaps:

var old = [];
for (var index = 0; index < arr.length; index+= 4)
 old.push( arr.slice(index, index + 4) );

Answer 2

var newArr = [];
while(arr.length){
 newArr.push(arr.splice(0,4));
}

• bopjesvla: This is very slow with big arrays, since every time the array has to be reindexed