PHP insert index as value in array

Question

How can I add to a multidimensional array also the index number of the current added item?

$data_array[] = array('data_array_index' => *the index number of the this array on $data_array*, 'stuff' => 'stuff', etc.)

So when I:

print_r($data_array);

Array(
  [0] => Array(
            data_array_index => 0
            stuff => stuff
         )
  [25] => Array(
            data_array_index => 25
            stuff => stuff
         )
  etc.

Thank you

EDIT

Should this work?

$data_array[] = array('data_array_index' => end($data_array)+1, 'stuff' => 'stuff', etc.)

you can't "add", you have to rebuild the array. array(0=>array('data_array_index'=>0,etc...)) — Marc B
– Marc B, Commented Oct 29, 2015 at 14:25
I'm inside a foreach loop, who rebuilds the array at each loop with the added data. BTW, this is not answering my question.... — Perocat
– Perocat, Commented Oct 29, 2015 at 14:31
Just a question, why do you need the key in data_array_index inside the array if you'll probably not be able to access it directly since you won't have the $data_array key to it? — FirstOne
– FirstOne, Commented Oct 29, 2015 at 14:40
I need later to access all data associated with key 'data_array_index' in all multidimensional arrays inside $data_array — Perocat
– Perocat, Commented Oct 29, 2015 at 14:44

Thaillie · Accepted Answer · 2015-10-29 14:59:06Z

1

You could do this:

$array = [
   0 => [ "data_array_index" => 0, "stuff" => "stuff" ],
   25 => [ "data_array_index" => 25, "stuff" => "stuff" ]
];

$array[] = array('data_array_index' => 0, 'stuff' => 'stuff')

end($array);
$last_id = key($array);

$array[$last_id]['data_array_index'] = $last_id;

I don't know why you want data_array_index in the array because if you put it in a foreach loop you can get the key without needing the variable.

Example:

foreach($key => $data) {
        ^^^^ The same as `data_array_index`
}

edited Oct 29, 2015 at 14:59

answered Oct 29, 2015 at 14:32

Thaillie

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3 Comments

Perocat Over a year ago

Inefficent for very large arrays

Thaillie Over a year ago

@Perocat, For as far as i know this is the fastest method.

Alex Blex Over a year ago

@Perocat, it is O(1), and can hardly be improved. Could you elaborate in which way it is inefficient ?

Daan · Accepted Answer · 2015-10-29 14:26:00Z

0

Suppose you have this array:

$data_array = [
   0 => [ "data_array_index" => 0, "stuff" => "stuff" ],
   25 => [ "data_array_index" => 25, "stuff" => "stuff" ]
];

Now to set a key (note the $data_array[100]):

$data_array[100] = [ "data_array_index" => 100, "stuff" => "stuff" ];

answered Oct 29, 2015 at 14:26

Daan

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4 Comments

Jan Over a year ago

I guess he wanted some kind of "automatism", as he doesn't know the key 100 in advance.

Daan Over a year ago

@Jan Then I miss understood.

Perocat Over a year ago

@Jan yes it's like you describled, it should be "automatic"

Jan Over a year ago

I guess there are only two possible solutions for an index: either the end (this can be calculated by count()) or if you splice the array. But in both ways you will end up knowing the index in advance, or am I wrong?

peter anderson · Accepted Answer · 2015-10-29 14:35:41Z

0

try this once

$arr=array(12=>array("stuff"=>"stuff1"),15=>array("stuff"=>"stuff2"));

foreach($arr as $key=>$val){
$arr[$key]['data_array_index']=$key;    
}

echo "<pre>"; print_r($arr);

answered Oct 29, 2015 at 14:35

peter anderson

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1 Comment

Perocat Over a year ago

Inefficent for very large arrays

Philipp Palmtag · Accepted Answer · 2015-10-29 14:49:20Z

For my solution see the code below. Beware that this is a very rudimentary function now. It does not provide any fail safe or fallback. If you delete a key it will to fill the space etc.

<?php

// data array
$data_array = [];

// additional info for the array
$info_a = "Lorem Ipsum";
$info_b = "Lorem Ipsum";

// call function
addElement($data_array, $info_a);
addElement($data_array, $info_b);

// display output
echo '<pre>';
print_r($data_array);
echo '</pre>';

function addElement(&$array, $info)
{
    // add info to the array
    $array[] = [
        'stuff'=>$info
    ];

    // get the key of the current array
    end($array);
    $key = key($array);

    // add this information to the array
    $array[$key]['data_array_index'] = $key;
}
?>

Output would be

Array
(
    [0] => Array
        (
            [stuff] => Lorem Ipsum
            [data_array_index] => 0
        )

    [1] => Array
        (
            [stuff] => Lorem Ipsum
            [data_array_index] => 1
        )

)

Nishanth Matha · Accepted Answer · 2015-10-29 15:17:54Z

0

Use array_walk

array_walk($data_array,function($value,$key)use($new_array) {
    $value['data_array_index'] = $key;
    $new_array[$key]=$value;
});

working demo: http://phpfiddle.org/main/code/p937-7cue

edited Oct 29, 2015 at 15:17

answered Oct 29, 2015 at 14:42

Nishanth Matha

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