How to avoid loop inside loop

Question

I have this code:

foreach($categories as $category) {
  $items = getItems($category);

  foreach($items as $item) {
     // some code to manipulate $item
  }
}

As you can see, inner loop depends on outer loop. Problem is that if data is too big, this takes quite some time. Is there some way, algorithm or technique so that I can avoid inner loop that is dependent on outer loop ?

PS. I am using PHP 5.3 so yield is out of question. Also someone told me that may be recursion can be helpful here but I don't exactly know how to go about with that.

Thanks for the help

With what you've provided, I can't see any way to algorithmically avoid this. You can possibly tweak the workflow of what you're trying to do so that you don't have to manipulate the items of every category at once and instead just do a single category at a time — Jeff Lambert
– Jeff Lambert, Commented May 8, 2015 at 20:09
If you can put your array code and what you expected as an output then anyone can suggest the solution — Death-is-the-real-truth
– Death-is-the-real-truth, Commented May 8, 2015 at 20:12
not make sense. it depends on the case. what's your desired output. Some time same output can get without inner loop and some time it's necessary. — Death-is-the-real-truth
– Death-is-the-real-truth, Commented May 8, 2015 at 20:19

Uri Goren · Accepted Answer · 2015-05-08 20:21:29Z

2

One way is to avoid the nested loops is to store the data first, an then manipulate it

$items=array_map("getItems",$categories);
$items=array_reduce("array_merge",$items);
array_walk($items,"item_manipulation");

Note that this code is not more efficient than your original snippet, it's just without nested loops as you asked.

A more intelligent optimization would be (maybe) possible if we could know what getItems does, and what per-item manipulation you do

answered May 8, 2015 at 20:21

Uri Goren

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