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?

Just for fun in JavaScript 1.6 (maybe jQuery) arr.join().match(/\d+,\d+,\d+,\d+/g).map(function(s) { return s.split(",") } ) — Jonas Elfström
– Jonas Elfström, Commented May 3, 2011 at 12:46
Isn't it a possibility to work with one format? Saves a lot of looping. — Blaise
– Blaise, Commented Jan 10, 2013 at 14:04

zacharykane · Accepted Answer · 2013-08-12 15:44:21Z

1

Something like this, perhaps:

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

zacharykane

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answered May 3, 2011 at 11:03

Mike Thomsen

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Comments

Van Coding · Accepted Answer · 2011-05-03 11:04:58Z

1

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

answered May 3, 2011 at 11:04

Van Coding

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