Get only the array elements with certain keys

Question

Possible Duplicate:
Pattern Match on a Array Key

I need to get all the elements in an array with a specific key pattern. For example in this array:

$items = array(
   "a"         => "1",
   "b"         => "2",
   "special_1" => "3",
   "c"         => "4",
   "special_2" => "5",
   "special_3" => "6",
   "d"         => "7"
);

I would need all elements with a key containing the string special_. These should define a new array:

$special_items = array(
   "special_1" => "3",
   "special_2" => "5",
   "special_3" => "6",
);

Is there a smart method besides a while loop?

duplicate of https://stackoverflow.com/questions/10583591/how-to-get-a-subset-of-post-array-with-keys-starting-with-a-prefix , my answer which provides a custom function named `preg_grep_keys()` may be useful to people interested in this question. — goat, Aug 08 '18 at 02:22

score 23 · Accepted Answer · answered Oct 14 '12 at 22:54

23

How about this?

$special_items = array();

foreach($items as $key => $val) {
    if(substr($key, 0, 8) == 'special_')
        $special_items[$key] = $val;
}

answered Oct 14 '12 at 22:54

Austin Brunkhorst

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2

Yep, the easiest to manage too. – Austin Brunkhorst Oct 14 '12 at 23:02

score 7 · Answer 2 · answered Oct 14 '12 at 22:56

7

First you need to get an array containing the keys. array_keys

Then, you need to filter the keys to find the ones you want. array_filter

Use this callback:

function($a) {return substr($a,0,8) == "special_";}

Then flip the array so that the keys are keys again instead of values. array_flip

Finally, intersect those keys with the original array. array_intersect_key

Result:

$special_items = array_intersect_key($items,array_flip(array_filter(array_keys($items),function($a) {return substr($a,0,8) == "special_";})));

answered Oct 14 '12 at 22:56

Niet the Dark Absol

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Yes, but a little bit more tricky than a simple for/if – Aubin Oct 14 '12 at 23:03
That’s exactly the generic solution I was looking for. I need to make it a utility function. Thanks. – Olivier 'Ölbaum' Scherler Aug 23 '17 at 12:46

score 5 · Answer 3 · edited Dec 29 '13 at 14:36

5

You can use FilterIterator

$iterator = new SpecialFilter($items, 'special');
var_dump(iterator_to_array($iterator));

Output

array
  'special_1' => string '3' (length=1)
  'special_2' => string '5' (length=1)
  'special_3' => string '6' (length=1)

Class Used

class SpecialFilter extends FilterIterator {
    private $f;
    public function __construct(array $items, $filter) {
        $object = new ArrayObject( $items );
        $this->f = $filter;
        parent::__construct( $object->getIterator() );
    }
    public function accept() {
        return 0 === strpos( $this->getInnerIterator()->key(), $this->f );
    }
}

edited Dec 29 '13 at 14:36

kaiser

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answered Oct 14 '12 at 22:58

Baba

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Yes! OO tech is the winner. Why make the thing simple when we can complicate them? 2 new, one inheritance (at least) to do 3 lines of code: for/if/doit – Aubin Oct 14 '12 at 23:06
1

`Is there a smart method besides a while loop?` Yes If `for/if/doit` is sufficient they would be nothing like `Iterators` – Baba Oct 14 '12 at 23:09
Nice, clean, test-able... +1 – kaiser Dec 29 '13 at 14:38
@Aubin Right, because who would want an easy to use and extend utility class when they can just copy paste blocks of code everywhere? I genuinely feel for anyone inheriting your code. Genuinely this is the best answer to OP's question. – Hybrid web dev Sep 28 '22 at 04:08

score 1 · Answer 4 · answered Oct 14 '12 at 22:53

1

$special_items = array_intersect_key(array_flip(preg_grep('/^special_\d+/', array_keys($items))), $items);

Please don't actually use that. Just use a foreach loop with strpos + an if statement like all normal people would.

answered Oct 14 '12 at 22:53

goat

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Well, exactly what I currently have. +1 – zerkms Oct 14 '12 at 22:55
Incorrect use of `array_intersect_key`. -1 – Niet the Dark Absol Oct 14 '12 at 22:58
Arguments in the wrong order. – Niet the Dark Absol Oct 14 '12 at 23:16

score 1 · Answer 5 · edited Oct 14 '12 at 22:59

1

how about

$keys = preg_grep( "/special_/i", array_keys( $items ) );

$new_array = array();

foreach( $keys as $k )
{
    $new_array[ $k ] = $items[ $k ];
}

edited Oct 14 '12 at 22:59

Aubin

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answered Oct 14 '12 at 22:56

Seth

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Get only the array elements with certain keys

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