Function similar to array_map to re-index an array

Question

I've recently been using array_map to replace this kind of code:

$users = ...;
$usersIds = array();
foreach ($users as $user) {
   $usersIds[] = $user->getId();
}

with

$users = ...;
$usersIds = array_map(function ($user) {
    return $user->getId();
}, $users);

It's more elegant, and i guess that this more efficient.

Now i'd like to know if the following code could be improved with a function similar to array_map:

$users = ...;
$indexedUsers = array();
foreach ($users as $user) {
    $indexedUsers[$user->getId()] = $user;
}

hakre · Accepted Answer · 2012-07-08 23:39:12Z

3

As you already have the keys, just combine it:

$indexedUsers = array_combine($usersIds, $users);

Apart from that, foreach normally is elegant, especially these trivial cases you outline don't need much function logic, so I'd prefer the iterator pattern here instead of going functional.

answered Jul 8, 2012 at 23:39

hakre

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1 Comment

Tadeck Over a year ago

I generally agree, so +1. There shouldn't be (much) performance gain / loss unless there is some more logic involved.

Matthew · Accepted Answer · 2012-07-08 23:38:02Z

First off, I doubt array_map() is faster than your original foreach loop. Never change code because you think it's faster. Of course, if you think it's more elegant and the speed difference is insignificant, then nobody should care.

You can often think of using iterators in these contexts:

class ArrayGetIdIterator extends ArrayIterator
{
  public function key()
  {
    return $this->current()->getId();
  }
}

$indexedUsers = iterator_to_array(new ArrayGetIdIterator($users));

To minimize boilerplate code and maximize reusability, the constructor could accept some type of arguments (e.g, which function to call) and you could create a static helper.

Although, personally, I would just take your original code, wrap it into a reusable function and call it a day.

Chris Trahey · Accepted Answer · 2012-07-09 00:16:39Z

1

You can build on your former success and use array_combine...

$get_user_id = function($user) {return $user->getId();};
$indexedUsers = array_combine(array_map($get_user_id, $users), $users);

edited Jul 9, 2012 at 0:16

answered Jul 8, 2012 at 23:33

Chris Trahey

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3 Comments

AdrienBrault Over a year ago

array_walk returns a boolean, and array_combine expects the first argument to be an array. Your code does not work.

Chris Trahey Over a year ago

My apologies, that's a typo; it was meant to mirror your code and be array_map...

Chris Trahey Over a year ago

As evident in the order of parameters :-) Change has been made.

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