PHP - Filtering an array to delete the values with non-similar keys from sub-arrays

Question

I have an array like below. This is coming from a centralised database and I have no way of knowing beforehand what the actual array will contain. I want to compare the sub-arrays on keys and that is why want to delete the keys which are not present is all sub-arrays.

Array (
    [0] => Array
        (
            [a] => 
            [b] => 8
            [c] => 1
            [d] => taille-8
            [e] => 
            [k] => taill
        )

    [1] => Array
        (
            [a] => 
            [b] => 7
            [c] => 2
            [d] => taille-7
            [f] =>
            [k] => tafefef
        )

    [2] => Array
        (
            [a] => ce
            [b] => 34
            [c] => 2
            [d] => taille-34
            [g] => dee
            [k] => tacefef
        ) );

I want to delete the keys which are not repeating in all sub-arrays. In the above example they are 'e', 'f' and 'g'. This needs to happen dynamically.

Array (
    [0] => Array
        (
            [a] => 
            [b] => 8
            [c] => 1
            [d] => taille-8
            [k] => taill
        )

    [1] => Array
        (
            [a] => 
            [b] => 7
            [c] => 2
            [d] => taille-7
            [k] => tafefef
        )

    [2] => Array
        (
            [a] => ce
            [b] => 34
            [c] => 2
            [d] => taille-34
            [k] => tacefef            
        ) );

Any suggestion is appreciated.

How do you create the first array. if you creating it you can ignore those keys right? did you try that? — Lahiru Madhusanka
– Lahiru Madhusanka, Commented Aug 24, 2018 at 5:49
Have a look at php.net/manual/en/function.array-intersect-key.php — JasonB
– JasonB, Commented Aug 24, 2018 at 5:53
@LahiruMadusanka The array is coming from a database which is getting updated regularly. Not in my control and also I cannot know beforehand which keys will be there. — Sam11
– Sam11, Commented Aug 24, 2018 at 5:58

Martin Cook · Accepted Answer · 2018-08-24 06:18:18Z

3

You can use argument unpacking. If your array is stored in $a, then the following should work:

// create an array with only the keys that are common to all subarrays
$new = array_intersect_key(...$a);

// prune original array
foreach ($a as &$arr) {
    $arr = array_intersect_key($new, $arr);
}

edited Aug 24, 2018 at 6:18

answered Aug 24, 2018 at 6:12

Martin Cook

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Comments

Andreas · Accepted Answer · 2018-08-24 06:10:16Z

0

You can splice the array and loop the rest.
In the loop I overwrite the $new with whatever is the same in each iteration.
The end should be what is matching throughout the full array.

Then we need to use the new and as a template to remove the other items in the array, so we loop again and intersect again but overwrite $arr this time.

$arr =[['a' => 1, 'b' => 2, 'c' => 3],
       ['a' => 1, 'c' => 3],
       ['c' => 3]];

$new = $arr[0];

foreach($arr as $sub){
    $new = array_intersect_key($new, $sub);
}
foreach($arr as &$sub){
    $sub =array_intersect_key($sub, $new);
}
unset($sub);
Var_dump($arr);

Output

array(3) {
  [0]=>
  array(1) {
    ["c"]=>
    int(3)
  }
  [1]=>
  array(1) {
    ["c"]=>
    int(3)
  }
  [2]=>
  &array(1) {
    ["c"]=>
    int(3)
  }
}

https://3v4l.org/oM3M1l

edited Aug 24, 2018 at 6:10

answered Aug 24, 2018 at 5:50

Andreas

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3 Comments

Sam11 Over a year ago

Thank you for you answer. I do not want to change the actual structure of the array. So the result i was should look like $new =[ ['c' => 3], ['c' => 3], ['c' => 3]];

Andreas Over a year ago

In that case I think we need to loop twice see updated code.

Andreas Over a year ago

@sam11 No problem!

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