Exception or error:
I’m looking for an array function that does something like this:
$myArray = array(
'apple'=>'red',
'banana'=>'yellow',
'lettuce'=>'green',
'strawberry'=>'red',
'tomato'=>'red'
);
$keys = array(
'lettuce',
'tomato'
);
$ret = sub_array($myArray, $keys);
where $ret is:
array(
'lettuce'=>'green',
'tomato'=>'red'
);
A have no problem in writing it down by myself, the thing is I would like to avoid foreach loop and adopt a built-in function or a combination of built-in functions. It seems to me like a general and common array operation – I’d be surprised if a loop is the only option.
How to solve:
This works:
function sub_array(array $haystack, array $needle)
{
return array_intersect_key($haystack, array_flip($needle));
}
$myArray = array(
'apple'=>'red',
'banana'=>'yellow',
'lettuce'=>'green',
'strawberry'=>'red',
'tomato'=>'red'
);
$keys = array(
'lettuce',
'tomato'
);
$ret = sub_array($myArray, $keys);
var_dump($ret);
Answer：
You can use array_intersect_key, but it uses second array with keys and values. It computes the intersection of arrays using keys for comparison
<?php
$array1 = array('blue' => 1, 'red' => 2, 'green' => 3, 'purple' => 4);
$array2 = array('green' => 5, 'blue' => 6, 'yellow' => 7, 'cyan' => 8);
$array3 = array('green' => '', 'blue' => '', 'yellow' => '', 'cyan' => '');
$array4 = array('green', 'blue', 'yellow', 'cyan');
var_dump(array_intersect_key($array1, $array2));
var_dump(array_intersect_key($array1, $array3));
var_dump(array_intersect_key($array1, $array4));
?>
The above example will output:
array(2) {
["blue"]=>
int(1)
["green"]=>
int(3)
}
array(2) {
["blue"]=>
int(1)
["green"]=>
int(3)
}
array(0) {
}
Answer：
$ret = array_filter($myArray, function ($key) use ($keys) { return in_array($key, $keys); }, ARRAY_FILTER_USE_KEY);
Answer：
One-liner:
$subArray = array_intersect_key($items, array_fill_keys($keys, 1));
Example:
<?php
$items = [ 'product_id' => 1234, 'color' => 'green', 'qty' => 5, 'desc' => 'Shirt' ];
$keys = [ 'product_id', 'desc' ];
$subArray = array_intersect_key($items, array_fill_keys($keys, 1));
var_dump($subArray);
Produces:
array(2) {
["product_id"]=>
int(1234)
["desc"]=>
string(5) "Shirt"
}
Works with:
- numerical keys,
- associative arrays,
- mixed arrays,
- arrays with non-unique values