Limit the amount of items in a loop

Question

I'm trying to build an array of a type of data in my database. The problem is there are tens of thousands of items in the resultant array, which is too much for my system to handle.

I'd like to limit the array size to no more than 500 items.

My code is here:


public function deleteTermByVid($vid) {
  $terms = [];
  $controller = $this->entityTypeManager->getStorage('taxonomy_term');
  $tree = $controller->loadTree($vid);
  foreach ($tree as $term) {
    $terms[] = $term->tid;
  }
  $entities = $controller->loadMultiple($terms);
  $controller->delete($entities);
  return count($terms);
}

I've reviewed these SO issues: PHP: Limit foreach() statement? Limit this PHP foreach statement to just 5 loops ...but haven't had success in limiting the $terms array.

If you have any ideas about a way to limit $terms[] to no more than 500 terms, please let me know.

++ Updated code for @Barmar:

public function deleteTermByVid($vid) {
  $terms = [];
  $controller = $this->entityTypeManager->getStorage('taxonomy_term');
  $tree = $controller->loadTree($vid);
  foreach ($tree as $term) {
    $terms[] = $term->tid;
  }
  $terms = array_slice($terms, 0, 5); /* ____NEW LINE ___ */
  $entities = $controller->loadMultiple($terms);
  $controller->delete($entities);
  return count($terms);
}

You should limit the results from the database (something like `LIMIT` in MySQL) instead of trying to fix it in PHP after you've fetched all the data. Only fetch the columns you need and the number of records you want. Fetching thousands of records just to discard most of them is just unnecessary overhead. — M. Eriksson, Sep 21 '22 at 19:44
The solutions in the linked questions should have worked. E.g. `$tree = array_slice($tree, 0, 500);` What happened when you tried? — Barmar, Sep 21 '22 at 20:05
Hi @Barmar - I've tried this (please see note above - the comment wasn't formatted well)Is that the correct place to add the array_slice()? — scaffolding, Sep 21 '22 at 20:30
That's unreadable. Edit the question so you can format it properly. — Barmar, Sep 21 '22 at 20:32

score 1 · Accepted Answer · answered Sep 21 '22 at 20:34

1

You're slicing the wrong array, it should be $tree.

public function deleteTermByVid($vid) {
  $terms = [];
  $controller = $this->entityTypeManager->getStorage('taxonomy_term');
  $tree = $controller->loadTree($vid);
  $tree = array_slice($tree, 0, 5);
  foreach ($tree as $term) {
    $terms[] = $term->tid;
  }
  $entities = $controller->loadMultiple($terms);
  $controller->delete($entities);
  return count($terms);
}

answered Sep 21 '22 at 20:34

Barmar

741,623
53
500
612

You solved it. Thank you @barmar – scaffolding Sep 21 '22 at 20:38

score 1 · Answer 2 · answered Sep 21 '22 at 20:48

First of all, it is not logical to load a huge amount of data and then process and limit them in php. It makes the task slower, and wastes the server resources a little bit more. The best practice is to limit them in your mySql query. If you want to do the job by any means, there are a couple of ways possible to do the task for you: Using array_slice is the first option:

 $tree = array_slice($tree, 0, 5);

Second option is using while for your loop and not foreach. I don't know anything about the content of $tree, but lets suppose it is an array like the following:

$tree = ["A", "B", "C", "D", "E", "F"];

In this case it will be really easy to limit the items you want to get out of this array using while loop. Pay attention to the following:

$i = 0;
while ($i < 3)
{
    // Do whatever you wish here...
    echo $tree[$i] .PHP_EOL;
    $i++;
}

In this scenario, you can get just three items out of your array. Pretty easy!

Limit the amount of items in a loop

2 Answers2