Remove blacklist keys from array in PHP

Question

I have an associative array of data and I have an array of keys I would like to remove from that array (while keeping the remaining keys in original order -- not that this is likely to be a constraint).

I am looking for a one liner of php to do this.
I already know how I could loop through the arrays but it seems there should be some array_map with unset or array_filter solution just outside of my grasp.

I have searched around for a bit but found nothing too concise.

To be clear this is the problem to do in one line:

//have this example associative array of data
$data = array(
    'blue'   => 43,
    'red'    => 87,
    'purple' => 130,
    'green'  => 12,
    'yellow' => 31
);

//and this array of keys to remove
$bad_keys = array(
    'purple',
    'yellow'
);

//some one liner here and then $data will only have the keys blue, red, green

Make a function to do it: remove_keys_from_array($array, $keys). And look at that, it takes up only one line! — Blender
– Blender, Commented Jun 14, 2012 at 4:46
I know but I bet there is some way to use the php functions to do it... but fair enough, it does take only one line — hackartist
– hackartist, Commented Jun 14, 2012 at 4:47
Related: Remove key from array if key is in another array The inverse of this question: How do I remove keys from an array which are not in another array? — mickmackusa
– mickmackusa ♦, Commented Sep 15, 2023 at 7:33

Dharman · Accepted Answer · 2024-11-13 16:30:33Z

154

$out = array_diff_key($data, array_flip($bad_keys));

All I did was look through the list of Array functions until I found the one I needed (_diff_key).

edited Nov 13, 2024 at 16:30

Dharman♦

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answered Jun 14, 2012 at 4:50

Niet the Dark Absol

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2 Comments

TerryE Over a year ago

I had to think about this one for a mo. The point is $bad_keys = array(0=>'purple',1=>'yellow') so the keys in the array_flip are 'purple','yellow'. Hence the diff_key works. Neat. Thanks Kolink.

Stphane Over a year ago

I once needed to remove by value (not keys) and I ended up with this: $myArr = array(5, 25, 5, 30); ... THEN ... $myArr =& array_diff_key($myArr, array_flip(array_keys($myArr, 5)));

Community · Accepted Answer · 2017-05-23 12:10:30Z

39

The solution is indeed the one provided by Niet the Dark Absol. I would like to provide another similar solution for anyone who is after similar thing, but this one uses a whitelist instead of a blacklist:

$whitelist = array( 'good_key1', 'good_key2', ... );
$output = array_intersect_key( $data, array_flip( $whitelist ) );

Which will preserve keys from $whitelist array and remove the rest.

edited May 23, 2017 at 12:10

CommunityBot

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answered Jan 3, 2016 at 9:21

Peyman Mohamadpour

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1 Comment

mickmackusa Over a year ago

This answer has been posted on the wrong page; it doesn't do what this page is asking for. It is suitable (and already posted) on this earlier page: How do I remove keys from an array which are not in another array?

TarranJones · Accepted Answer · 2016-04-25 11:10:25Z

0

This is a blacklisting function I created for associative arrays.

if(!function_exists('array_blacklist_assoc')){

    /**
     * Returns an array containing all the entries from array1 whose keys are not present in any of the other arrays when using their values as keys.
     * @param array $array1 The array to compare from
     * @param array $array2 The array to compare against
     * @return array $array2,... More arrays to compare against
     */

    function array_blacklist_assoc(Array $array1, Array $array2) {
        if(func_num_args() > 2){
            $args = func_get_args();
            array_shift($args);
            $array2 = call_user_func_array('array_merge', $args);
        } 
        return array_diff_key($array1, array_flip($array2));
    }
}

$sanitized_data = array_blacklist_assoc($data, $bad_keys);

answered Apr 25, 2016 at 11:10

TarranJones

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1 Comment

mickmackusa Over a year ago

Modern PHP affords more concise (less convoluted) syntax with the spread operator.

function remove_blacklisted_keys(array $haystack, array ...$blacklists) {     return array_diff_key($haystack, array_flip(array_merge(...$blacklists))); }

TylerH · Accepted Answer · 2024-11-13 17:27:05Z

-1

array_filter() is more readable, in my opinion.

Here's how I'd do it:

$data = array_filter($data, function($k) use ($bad_keys) {return !in_array($k, $bad_keys);}, ARRAY_FILTER_USE_KEY);

edited Nov 13, 2024 at 17:27

TylerH

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answered Sep 15, 2023 at 6:12

Supriya Rajgopal

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1 Comment

mickmackusa Over a year ago

PHP consistently performs worse when making "values" checks (e.g. in_array(), array_search()) versus making "key" checks (e.g. array_intersect_key(), isset(), key_exists()). This answer is not likely to outperform other, earlier answers on this page. This answer will make N calls of in_array(), but other answers on this page do not make iterated function calls. A Stack Overflow answer must never contain Hope this helps -- it is irrelevant to the page; no signoffs or esignatures. Modern concise code: $data = array_filter($data, fn($k) => !in_array($k, $bad_keys), ARRAY_FILTER_USE_KEY);

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