Move Value in PHP Array to the Beginning of the Array

Question

I have a PHP array similar to this:

0 => \"red\",
1 => \"green\",
2 => \"blue\",
3 => \"yellow\"

I want to move yellow to index

Answer 1

$a = array('red','green', 'blue','yellow');

$b = array_reverse( $a );

If your question is how to make the last become the first.

Answer 2

This seems like the simplest way to me. You can move any position to the beginning, not just the last (in this example it moves blue to the beginning).

$colours = array("red", "green", "blue", "yellow");

$movecolour = $colours[2];
unset($colours[2]);
array_unshift($colours, $movecolour);

Answer 3

Probably the most straightforward way

array_unshift( $arr, array_pop( $arr ) );

EDIT

Per your comment "how can I take any one subscript from the array and move it to the beginning", my answer above doesn't fully satisfy that request - it only works by moving the last element to the 0 index.

This function, however, does satisfy that request

/**
 * Move array element by index.  Only works with zero-based,
 * contiguously-indexed arrays
 *
 * @param array $array
 * @param integer $from Use NULL when you want to move the last element
 * @param integer $to   New index for moved element. Use NULL to push
 * 
 * @throws Exception
 * 
 * @return array Newly re-ordered array
 */
function moveValueByIndex( array $array, $from=null, $to=null )
{
  if ( null === $from )
  {
    $from = count( $array ) - 1;
  }

  if ( !isset( $array[$from] ) )
  {
    throw new Exception( "Offset $from does not exist" );
  }

  if ( array_keys( $array ) != range( 0, count( $array ) - 1 ) )
  {
    throw new Exception( "Invalid array keys" );
  }

  $value = $array[$from];
  unset( $array[$from] );

  if ( null === $to )
  {
    array_push( $array, $value );
  } else {
    $tail = array_splice( $array, $to );
    array_push( $array, $value );
    $array = array_merge( $array, $tail );
  }

  return $array;
}

And, in usage

$arr = array( 'red', 'green', 'blue', 'yellow' );

echo implode( ',', $arr ); // red,green,blue,yellow

// Move 'blue' to the beginning
$arr = moveValueByIndex( $arr, 2, 0 );

echo implode( ',', $arr ); // blue,red,green,yellow

Answer 4

EDITED

This is an update based on the question and liking the generic aspects of the answer by Peter Bailey. However, the code is too function/memory intensive for me so below just does a simple swap of the $from and $to values. This method does not cause the array in question to be resized at all, it simply swaps to values within it.

Second Edit: I added in some more argument checking as mentioned in the comments.

function moveValueByIndex( array $array, $from=null, $to=null )
{
  // There is no array, or there are either none or a single entry
  if ( null === $array || count($array) < 2 )
  {
    // Nothing to do, just return what we had
    return $array;
  }

  if ( null === $from )
  {
    $from = count( $array ) - 1;
  }

  if ( null === $to )
  {
    $to = 0;
  }

  if ( $to == $from )
  {
    return $array;
  }

  if ( !array_key_exists($from, $array) )
  {
    throw new Exception( "Key $from does not exist in supplied array." );
  }

  $value = $array[$from];
  $array[$from] = $array[$to];
  $array[$to] = $value;

  return $array;
}

Forgive me if I should have just added this in a comment to Peter's post.. it just was too long to inline all of this there :/

Answer 5

PHP: move any element to the first or any position:

$sourceArray = array(
    0 => "red",
    1 => "green",
    2 => "blue",
    3 => "yellow"
);
// set new order
$orderArray = array(
    3 => '',
    1 => '',
);
$result = array_replace($orderArray, $sourceArray);
print_r($result);

Answer 6

If you aren't always planning on bringing the very last object to the beginning of the array, this would be the most simplistic way to go about it...

$array = array('red','green','blue','yellow');
unset($array[array_search($searchValue, $array)]);
array_unshift($array, $searchValue);