Unset a row in a multidimensional array

Question

I have this array $output which looks like this:

Array(
    [0] => Array(
        [0] => 1a
        [1] => 1b
        [2] => 1c
    )
    [1] => Array(
        [0] => 2a
        [1] => 2b
        [2] => 2c
    )
    [2] => Array(
        [0] => 3a
        [1] => 3b
        [2] => 3c
    )
    [3] => Array(
        [0] => 4a
        [1] => 4b
        [2] => 4c
    )
)

and so on...

When I want to remove the second element I just use:

$output = unset($output[1]);

to get the following:

Array(
    [0] => Array(
        [0] => 1a
        [1] => 1b
        [2] => 1c
    )
    [1] => Array(
        [0] => 3a
        [1] => 3b
        [2] => 3c
    )
    [2] => Array(
        [0] => 4a
        [1] => 4b
        [2] => 4c
    )
)

My question is how to remove every second element of every element in the array ([0][1], [1][1], [2][1], [3][1] ,...) to get the following:

Array(
    [0] => Array(
        [0] => 1a
        [1] => 1c
    )
    [1] => Array(
        [0] => 2a
        [1] => 2c
    )
    [2] => Array(
        [0] => 3a
        [1] => 3c
    )
    [3] => Array(
        [0] => 4a
        [1] => 4c
    )
)

unset() doesn't return anything.

Álvaro González
– Álvaro González

2011-08-31 17:18:51 +00:00
Commented Aug 31, 2011 at 17:18 — Álvaro González
– Álvaro González, Commented Aug 31, 2011 at 17:18

Marc B · Accepted Answer · 2011-08-31 16:46:28Z

26

Can't be done with a simple command, but you can use a loop:

foreach(array_keys($output) as $key) {
   unset($output[$key][1]);
}

answered Aug 31, 2011 at 16:46

Marc B

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2 Comments

Mike Over a year ago

Very helpful, thanks! To add to your answer, if you want to keep your remaining keys sequential after the unset, you can include at the end of (and within) your foreach: $output[$key] = array_values($output[$key]);. The array_values() will rebase the keys so they are sequential starting from zero.

mickmackusa Over a year ago

If you want to reindex after unsetting, just call array_splice() as @cwallen demonstrates.

Dandi Darmawan · Accepted Answer · 2020-08-20 16:12:37Z

12

Clean and neat:

$f = function(&$a,$k) { unset($a[1]); };
array_walk($arr, $f);

Or:

array_walk($arr, function (&$a, $k) {
  unset($a[1]); 
});

edited Aug 20, 2020 at 16:12

Dandi Darmawan

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answered Aug 31, 2011 at 16:53

dnagirl

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1 Comment

mickmackusa Over a year ago

Why declare $k? You never use it.

Arnaud Le Blanc · Accepted Answer · 2011-08-31 16:46:00Z

8

You can iterate over the array, and unset() what you want in each sub-array:

foreach($output as &$item) {
    unset($item[2]);
}
unset($item); // unset reference

answered Aug 31, 2011 at 16:46

Arnaud Le Blanc

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1 Comment

sMyles Over a year ago

Make sure you include the & like arnaud has above, this is required to reference it when you call unset

cwallenpoole · Accepted Answer · 2011-08-31 16:48:24Z

2

You'd use a combination of array_map and array_splice:

function removeSecond( array &$arr )
{
    array_splice( $arr, 1, 1 );
}
$out = array_map( 'removeSecond', $input );

The problem with unset is that it will leave the indexes as they were:

$ php -r '$arr = array(array(0,1,2)); unset($arr[0][1]); var_dump($arr);'
array(1) {
  [0]=>
  array(2) {
    [0]=>
    int(0)
    [2]=>
    int(2)
  }
}

While splice will update the indexes:

$ php -r '$arr = array(array(0,1,2)); array_splice($arr[0], 1, 1); var_dump($arr);'
array(1) {
  [0]=>
  array(2) {
    [0]=>
    int(0)
    [1]=>
    int(2)
  }
}

answered Aug 31, 2011 at 16:48

cwallenpoole

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Comments

cwallenpoole · Accepted Answer · 2011-08-31 16:52:35Z

1

foreach($array as $key=>$val){ unset($val[1]); }

edited Aug 31, 2011 at 16:52

cwallenpoole

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answered Aug 31, 2011 at 16:47

FabioG

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1 Comment

mickmackusa Over a year ago

This code-only answer does not affect the original $array, but an element within a copy of $array. Within $val, the 1-keyed element will be removed, but $array is never mutated. Proof: 3v4l.org/aZ52f

T.Todua · Accepted Answer · 2021-07-31 07:26:29Z

0

I use this:

public function array_unset_key_in_children($array, $keyToUnsetInChildren)
{ 
    $newArray = [];
    foreach($array as $key=>$subArray) { 
        unset($subArray[$keyToUnsetInChild]);
        $newArray[$key] = $subArray;
    }
    return $newArray;
}

edited Jul 31, 2021 at 7:26

answered Apr 11, 2021 at 18:35

T.Todua

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2 Comments

T.Todua Over a year ago

@mickmackusa thanks, I've removed "array_key_exists" before unset, but about mutation - I had a case (couldnt explain why but it was hundred percent case) that mutating original array ended up using several times more memory (causing "memory exhausted, trying to allocate..." ) while creating new arrays did go incomparably easier. Had been debugging that case for a day, and this ended for sure to me.

mickmackusa Over a year ago

Okay. You might like to explain the benefit of your snippet in your answer.

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