Although an array in PHP is "a type that associates values to keys" and some say it's not possible to remove the keys, you might, in a sense, remove the keys from an array either replacing the keys or replacing the array with another array.

I suppose you would like to change the array to an array equivalent to an array initialized without explicit keys. For instance, you might have this array:

$arr = array(2 => 'a', 3 => 'b', 4 => 'c');

But you'd like it to be equivalent to:

$arr = array('a', 'b', 'c');

It's possible to do it using the function "array_values", like this:

$arr = array_values($arr);

Notice, though, the array still has keys: 0, 1, 2, and 3.

It's important to note that the integer keys are not the same as the array indexes. For instance, this piece of code:

<?php
$arr = array(3 => '', 4 => '', 1 => '', 2 => '');
foreach(k => $v):
    echo "$k ";
endforeach;

will output:

3 4 1 2

The function "array_values" might be used to make sure the keys values and indexes are the same:

<?php
    $arr = array(3 => '', 4 => '', 1 => '', 2 => '');
    foreach(array_values(k => $v):
        echo "$k ";
    endforeach;
    // outputs: 0, 1, 2, 3

I explained how to "remove" the keys, but you might want to implement a class for the topics, make an interface for topic contents (animations, images, etc.) and check the SPL data structures.

There are different ways to delete an array element, where some are more useful for some specific tasks than others.

Deleting a Single Array Element

If you want to delete just one single array element you can use unset() and alternatively array_splice().

By key or by value?

If you know the value and don't know the key to delete the element you can use array_search() to get the key. This only works if the element doesn't occur more than once, since array_search() returns the first hit only.

unset() Expression

Note: When you use unset() the array keys won’t change. If you want to reindex the keys you can use array_values() after unset(), which will convert all keys to numerically enumerated keys starting from 0 (the array remains a list).

Example Code:

$array = [0 => "a", 1 => "b", 2 => "c"];
unset($array[1]);
          // ↑ Key of element to delete

Example Output:

[
    [0] => a
    [2] => c
]

array_splice() Function

If you use array_splice() the (integer) keys will automatically be reindex-ed, but the associative (string) keys won't change — as opposed to array_values() after unset(), which will convert all keys to numerical keys.

Note: array_splice() needs the offset, not the key, as the second parameter; offset = array_flip(array_keys(array))[key].

Example Code:

$array = [0 => "a", 1 => "b", 2 => "c"];
array_splice($array, 1, 1);
                  // ↑ Offset of element to delete

Example Output:

[
    [0] => a
    [1] => c
]

array_splice(), same as unset(), take the array by reference. You don’t assign the return values back to the array.

Deleting Multiple Array Elements

If you want to delete multiple array elements and don’t want to call unset() or array_splice() multiple times you can use the functions array_diff() or array_diff_key() depending on whether you know the values or the keys of the elements to remove from the array.

array_diff() Function

If you know the values of the array elements which you want to delete, then you can use array_diff(). As before with unset() it won’t change the keys of the array.

Example Code:

$array = [0 => "a", 1 => "b", 2 => "c", 3 => "c"];
$array = array_diff($array, ["a", "c"]);
                         // └────────┘
                         // Array values to delete

Example Output:

[
    [1] => b
]

array_diff_key() Function

If you know the keys of the elements which you want to delete, then you want to use array_diff_key(). You have to make sure you pass the keys as keys in the second parameter and not as values. Keys won’t reindex.

Example Code:

$array = [0 => "a", 1 => "b", 2 => "c"];
$array = array_diff_key($array, [0 => "xy", "2" => "xy"]);
                              // ↑           ↑
                              // Array keys of elements to delete

Example Output:

[
    [1] => b
]

If you want to use unset() or array_splice() to delete multiple elements with the same value you can use array_keys() to get all the keys for a specific value and then delete all elements.

array_filter() Function

If you want to delete all elements with a specific value in the array you can use array_filter().

Example Code:

$array = [0 => "a", 1 => "b", 2 => "c"];
$array = array_filter($array, static function ($element) {
    return $element !== "b";
    //                   ↑
    // Array value which you want to delete
});

Example Output:

[
    [0] => a
    [2] => c
]

You can use array_values to accomplish this

$array = array ( 0 => 2088, 1 => 2087, 2 => 2091, 3 => 2083, 4 => 2086, 5 => 2085, 6 => 2084, 7 => 2092, 8 => 2089, 10 => 2122, 11 => 2122 );
$newarray = array_values($array);
var_dump($newarray);

http://codepad.org/rQkKOp0k

You need array_values($b) in order to re-key the array so the keys are sequential and numeric (starting at 0).

The following should do the trick:

$b = array(123,456,789,123);
unset($b[1]);
$b = array_values($b);
echo "<pre>"; print_r($b);

$out = array_diff_key($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).

Main is not the element of array, its a part of a element of array

function array_cleanup( $array, $todelete )
{
    $cloneArray = $array;
    foreach( $cloneArray as $key => $value )
    {
        if (strpos($value, $todelete ) !== false)   
           unset( $array[ $key ] );     //$array[$key] = str_replace($toDelete, $replaceWith, $value) ;  // add one more argument $replaceWith to function 

    }
    return $array;
}

Edit:

with array

function array_cleanup( $array, $todelete )
    {
      foreach($todelete as $del){
        $cloneArray = $array;
        foreach( $cloneArray as $key => $value )
        {          
            if (strpos($value, $del ) !== false)   
               unset( $array[ $key ] );     //$array[$key] = str_replace($toDelete, $replaceWith, $value) ;  // add one more argument $replaceWith to function 

           }
    }
     return $array;
}

  $newarray = array_cleanup( $cats, array('Category:Main') );