PHP: Move associative array element to beginning of array

Question

What would be the best method of moving any element of an associative array to the beginning of the array?

For example, say I have the following array:

$myArray = array(
    'two'   => 'Blah Blah Blah 2',
    'three' => 'Blah Blah Blah 3',
    'one'   => 'Blah Blah Blah 1',
    'four'  => 'Blah Blah Blah 4',
    'five'  => 'Blah Blah Blah 5',
);

What i want to do is move the 'one' element to the beginning and end up with the following array:

$myArray = array(
    'one'   => 'Blah Blah Blah 1',
    'two'   => 'Blah Blah Blah 2',
    'three' => 'Blah Blah Blah 3',
    'four'  => 'Blah Blah Blah 4',
    'five'  => 'Blah Blah Blah 5',
);

joeljpa · Accepted Answer · 2020-09-02 08:22:04Z

212

You can use the array union operator (+) to join the original array to a new associative array using the known key (one).

$myArray = array('one' => $myArray['one']) + $myArray;
// or      ['one' => $myArray['one']] + $myArray;

Array keys are unique, so it would be impossible for it to exist in two locations.

See further at the doc on Array Operators:

The + operator returns the right-hand array appended to the left-hand array; for keys that exist in both arrays, the elements from the left-hand array will be used, and the matching elements from the right-hand array will be ignored.

edited Sep 2, 2020 at 8:22

joeljpa

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answered Jun 30, 2012 at 17:55

Mark Eirich

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1 Comment

Mark Eirich Over a year ago

@andrewtweber No, I don't, but I did some testing and found that, compared to Emil's approach, it is 3x faster and takes half as much memory. I also found that it takes 20% more time than moving the same element to the end of the array.

trante · Accepted Answer · 2013-06-24 10:36:44Z

7

If you have numerical array keys and want to reindex array keys, it would be better to put it into array_merge like this:

$myArray = array_merge(array($key => $value) + $myArray );

answered Jun 24, 2013 at 10:36

trante

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Comments

Sune · Accepted Answer · 2014-03-19 07:55:23Z

2

A bit late, but in case anyone needs it, I created this little snippet.

function arr_push_pos($key, $value, $pos, $arr) 
{
    $new_arr = array();
    $i = 1;

    foreach ($arr as $arr_key => $arr_value) 
    {
        if($i == $pos) 
            $new_arr[$key] = $value;

        $new_arr[$arr_key] = $arr_value;

        ++$i;
    }

    return $new_arr;
}

Just adjust it to suit your needs, or use it and unset the index to move. Works with associative arrays too.

answered Mar 19, 2014 at 7:55

Sune

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1 Comment

nzn Over a year ago

A correction: $new_arr[$arr_key] = $arr_value; Should be: if ($arr_key != $key) $new_arr[$arr_key] = $arr_value; But otherwise: excellent! 1up.

You Old Fool · Accepted Answer · 2017-06-21 18:06:15Z

2

Here's another simple one-liner that gets this done using array_splice():

$myArray = array_splice($myArray,array_search('one',array_keys($myArray)),1) + $myArray;

answered Jun 21, 2017 at 18:06

You Old Fool

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Comments

Eugene Kaurov · Accepted Answer · 2019-01-28 17:48:39Z

1

if you have 2 arrays, 1st has elements to move to the top of 2nd array of elements, you can use

$result = \array_replace($ArrayToMoveToTop, $myArray);

Here is a code sample:

//source array    
$myArray = [
    'two' => 'Blah Blah Blah 2',
    'three' => 'Blah Blah Blah 3',
    'one' => 'Blah Blah Blah 1',
    'four' => 'Blah Blah Blah 4',
    'five' => 'Blah Blah Blah 5',
];
// set necessary order
$orderArray = [
    'one' => '',
    'two' => '',
];
//apply it
$result = \array_replace($orderArray, $myArray);
\print_r($result);

edited Jan 28, 2019 at 17:48

answered Aug 5, 2017 at 20:33

Eugene Kaurov

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Comments

Mark Eirich · Accepted Answer · 2012-06-30 18:13:57Z

-2

There's a function in the comments of the PHP manual for array_unshift which can be used to add an element, with key, to the beginning of an array:

function array_unshift_assoc(&$arr, $key, $val)
{
    $arr = array_reverse($arr, true);
    $arr[$key] = $val;
    return array_reverse($arr, true);
}

Unset the element and reinsert it again with the above function:

$tmp = $myArray['one'];
unset($myArray['one']);
$myArray = array_unshift_assoc($myArray, 'one', $tmp);

A more general approach may be to use uksort to sort your array by keys and provide a sorting function of your own.

edited Jun 30, 2012 at 18:13

Mark Eirich

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answered Jun 30, 2012 at 17:58

Emil Vikström

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3 Comments

user1493356 Over a year ago

Hi - thanks for the answer, though i dont want to sort the array in any way. I want to be able to know an elements key and move only that specfic element to the beginning of the array

Mark Eirich Over a year ago

I think the "=" is a syntax error: return = array_reverse($arr, true);

Mark Eirich Over a year ago

Also, when I run your code I get an array with only one element in it... :-(

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