Split an array into arrays several times in php

Question

I have an array of divs (blog posts). Say 33 blog posts. My task is to split them first into pairs (wrap every other two divs by another) so that I had 17 divs (each containing a pair of blog posts, the last one may contain only one blog post) and then - I want these 15 pair-divs to be split again into groups of 5 (the last one again may contain fewer)... so that in the end I had 3 blocks each containing maximum of 5 blocks each containing two blog posts. Do I make myself clear enough?

Of course the total number of all the posts is unknown so I have to make it work automagically.

Searching for an answer I found out about the function named array_chunk which does exactly that - splits an array into arrays... in my case - I have to run this function twice. And it works perfectly :)

$posts = array( 1,2,3,4 ... 33 );
$pairs = array_chunk( $posts, 2 ) // $pairs will contain an array of 17 arrays each containing two elements
$wrap = array_chunk( $pairs, 5 ) // $wrap will contain an array of 3 arrays each containing an array of pairs

The only thing that bothers me is that when I output all the divs via foreach I happen to naturally have 3 nested foreaches... first to render 3 (or more) big wrappers - then - 5 pair wrappers and finally - a foreach to render two blog posts.

I am aware of another solution - to run a foreach once on an original array and arange some mathematical conditions (e.g. if( $i % 2 == 0 ) { //do stuff }) to open and close suitable divs at appropriate moments. Which I haven't been able to accomplish and would be really glad if someone could help me out with this one if this method is the one to follow.

My questions are as follows:

Is there a significant difference (in terms of performance) as to how many nested foreaches to run?
Is there some kind of a best practice as to which method to use in such situations? Or probably there is a totally different approach.

Peter · Accepted Answer · 2013-01-23 22:39:03Z

1

Is there a significant difference (in terms of performance) as to how many nested foreaches to run?

Lets say you have 100 posts. So it's 50 pairs, 10 wraps.

Nested foreach: 50 loops * 10 loops = 100 loops
Single big loop using %: 100 loops...

Same thing in both cases. And array_chunk usage will not cause any major difference in perfomance.

Benchmark: http://codepad.org/KtEchEmR (I believe comparision of byte is faster than interger)

Is there some kind of a best practice as to which method to use in such situations? Or probably there is a totally different approach.

No. But I would rather go for nested loops as it will looks cleaner for another programmer, and you are able to wrap a function around every sub-loop if you need

edited Jan 23, 2013 at 22:39

answered Jan 23, 2013 at 21:40

Peter

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2 Comments

skip405 Over a year ago

My calculations differ from yours, Peter :) It's 160 loops needed, not 100 in the nested example. (which is almost twice as many). Have a look at this fiddle if you will (html window is more representative) - jsfiddle.net/skip405/Bb7St/2

skip405 Over a year ago

you completely broke my logic ))) Thanks for the answer.

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