PHP。 按键排列数组元素

$key = "cat"
$array = array( dog,
                bird, 
                cat,
                moon );

Need order like this (by key): cat, dog, bird, moon.

$key = "cat" , so string "cat" need to be first element of array. How to do that?

You're not actually sorting, just moving something in the array to the beginning. It might be simpler but here is one way:

array_unshift($array, current(array_splice($array, array_search($key, $array), 1))); 

• array_search() finds the index of the element that contains $key
• array_splice() removes that element
• array_unshift() prepends that element to the array

All the above solutions will work fine with the provided input array

    $array  = array('dog','bird', 'cat','moon');

However if the input array in an associative array, then above solutions will not work. See the changed input array below:

    $array = array('frist' => 'foo', 'dog','bird', 'cat','moon', 'cat');

It will be handy to use the following function in case of performance. It does not have overhead of calling too many builtin PHP array functions. Moreover it will work both sequential and associative PHP arrays. See the code segment below:

Function definition

    function moveToTop($array, $key){
      foreach ($array as $index => $value) ($value != $key) ? $newArray[$index] = $value : '';
      array_unshift($newArray, $key);
      return $newArray;
    }

Function call

    moveToTop($array, $key)

Output

    Array
    (
        [0] => cat
        [frist] => foo
        [1] => dog
        [2] => bird
        [3] => moon
    )