Question

I have an array

$users    = array();

$users[0]['id']=1;
$users[0]['name']="user1";

$users[1]['id']=2;
$users[1]['name']="user2";

$users[2]['id']=3;
$users[2]['name']="user3";

And i need to extract id’s into another array $ids; such that

$ids[0]=1;
$ids[1]=2;
$ids[2]=3;

I know one way to do it…

$ids    = array();
foreach($users as $user){
   $ids[]  = $user['id'];
}

But

1.is it is the best way to doit?
2.is it possible to do it without loops.
3.is it is the fastest way….?

Answer 1

All the comments above address the question very well, but since noone has actually posted any actual answer, here’s some additional info (to justify my answering it):

• Is it the best way to do it?

Probably, but it is certainly the cleaner and most readable way to do it

• is it possible to do it without loops?

Yes, but as people have said, it’s only a trick, as loops will be used in the background.

• is it is the fastest way?

Now this calls for some investigation. I have recreated a similar array as yours, using 100000 entries:

for ($i=0;$i<100000;$i++) {
    $users[] = array('id' => rand(),
            'name' => 'default');
}

And ran a few tests using different cases:

1.Plain old for loop (the one you have used yourself):

$ids=array();
$t = microtime(true);
foreach ($users as $key => $value) {
    $ids[] = $value['id'];
} 
echo microtime(true)-$t;

This required 0.085” on average

2.Using array_walk():

$t = microtime(true);
array_walk($users, create_function('$v,$k,&$ids', '$ids[0][] = $v["id"];'), array(&$ids));
echo microtime(true)-$t;

This required on average 0.22” (the same when using $GLOBALS[‘ids’] instead of this “reference” hack)

3.Using splFixedArray:
This iterator is supposed to be faster than plain arrays. Indeed, the code above requires 0.075” on average:

$users = new SplFixedArray(100000);
for ($i=0;$i<100000;$i++) {
    $users[$i] = array('id' => rand(),
            'name' => 'default');
}
$ids=array();
$t = microtime(true);
foreach ($users as $key => $value) {
    $ids[$key] = $value['id'];
}
echo microtime(true)-$t;

While the code below, where we use splFixedArray for both arrays, performed even faster, around 0.062”:

$users = new SplFixedArray(100000);
for ($i=0;$i<100000;$i++) {
    $users[$i] = array('id' => rand(),
            'name' => 'default');
}
$ids=new SplFixedArray(100000);
$t = microtime(true);
foreach ($users as $key => $value) {
    $ids[$key] = $value['id'];
}
echo microtime(true)-$t;

So, the bottom line is that no, it’s not the fastest way, but it’s the best if you take into account all 3 parameters you posed in your initial question