Find array elements that have a certain key-name prefix - php

Question

I have an associative array with lots of elements and want to get a list of all elements that have a key name with a certain prefix.
Example:
$arr = array(
'store:key' => 1,
'user' => 'demo',
'store:foo' => 'bar',
'login' => true,
);
// this is where I need help with:
// the function should return only elements with a key that starts with "store:"
$res = list_values_by_key( $arr, 'store:' );
// Desired output:
$res = array(
'store:key' => 1,
'store:foo' => 'bar',
);

Answer 1

You could simply do :
$arr = array(
'store:key' => 1,
'user' => 'demo',
'store:foo' => 'bar',
'login' => true,
);
$arr2 = array();
foreach ($arr as $array => $value) {
if (strpos($array, 'store:') === 0) {
$arr2[$array] = $value;
}
}
var_dump($arr2);
Returns :
array (size=2)
'store:key' => int 1
'store:foo' => string 'bar' (length=3)

Answer 2

This should work for you:
Just grab all keys which starts with store: with preg_grep() from your array. And then do a simple array_intersect_key() call to get the intersect of both arrays.
<?php
$arr = array(
'store:key' => 1,
'user' => 'demo',
'store:foo' => 'bar',
'login' => true,
);
$result = array_intersect_key($arr, array_flip(preg_grep("/^store:/", array_keys($arr))));
print_r($result);
?>
output:
Array
(
[store:key] => 1
[store:foo] => bar
)

Answer 3

From php 5.6 you can use array_filter:
$return = array_filter($array, function ($e) {
return strpos($e, 'store:') === 0;
}, ARRAY_FILTER_USE_KEY);
var_dump($return);
for earlier versions, you can use
$return = array_intersect_key($array, array_flip(array_filter(array_keys($array), function ($e) {
return strpos($e, 'store:') === 0;
})));
Demo.