Moving up/down an item in the array by its value

问题:

I cannot find an effective solution on rearranging/swapping an array item by its value by shifting by - 1 or + 1. I'm making an order on tables, if the user wants to shift the order by moving the value upwards or downwards, the array should swap the value of the desired item upwards or downwards, for example:

If the user wants to move the item order upwards:

$desired_item_to_move = 'banana';

$default_order = array('orange', 'apple', 'banana', 'pineapple', 'strawberry');

// Typically it should return this:

array('orange', 'banana', 'apple', 'pineapple', 'strawberry');

As you can see that banana and apple has been swapped, due to banana is moved upwards, if the user wants to move it down, it should swap pineapple to banana (from the first array) and so on.

I looked around on functions, array_replace was closest, but it only replaces arrays.

回答1:

Shifting up (assuming you've checked that the item is not already the first one):

$item = $array[ $index ];
$array[ $index ] = $array[ $index - 1 ];
$array[ $index - 1 ] = $item;

Shifting down:

$item = $array[ $index ];
$array[ $index ] = $array[ $index + 1 ];
$array[ $index + 1 ] = $item;

回答2:

A useful function for the more general problem of moving an element of an array from one position to another:

function array_move(&$a, $oldpos, $newpos) {
    if ($oldpos==$newpos) {return;}
    array_splice($a,max($newpos,0),0,array_splice($a,max($oldpos,0),1));
}

This can then be used to solve the specific problem in the original question:

// shift up
array_move($array,$index,$index+1);
// shift down
array_move($array,$index,$index-1);

Note, there's no need to check whether or not you're already at the start/end of the array. Note also, this function does not preserve the array keys - moving elements while preserving keys is more fiddly.

回答3:

$ret = array();
for ($i = 0; $i < count($array); $i++) {
    if ($array[$i] == $desired_item_to_move && $i > 0) {
        $tmp = array_pop($ret);
        $ret[] = $array[$i];
        $ret[] = $tmp;
    } else {
        $ret[] = $array[$i];
    }
}

This will move up all instances of the desired element, putting the new array into $ret.