柠檬铺

PHP5.5发布了，其中增加了一个新的数组函数array_column，感觉不错的！但是低版本PHP要使用，得自己实现：
参考地址：https://wiki.php.net/rfc/array_column

if(!function_exists('array_column')){
    function array_column($input, $columnKey, $indexKey=null){
        $columnKeyIsNumber      = (is_numeric($columnKey)) ? true : false;
        $indexKeyIsNull         = (is_null($indexKey)) ? true : false;
        $indexKeyIsNumber       = (is_numeric($indexKey)) ? true : false;
        $result                 = array();
        foreach((array)$input as $key=>$row){
            if($columnKeyIsNumber){
                $tmp            = array_slice($row, $columnKey, 1);
                $tmp            = (is_array($tmp) && !empty($tmp)) ? current($tmp) : null;
            }else{
                $tmp            = isset($row[$columnKey]) ? $row[$columnKey] : null;
            }
            if(!$indexKeyIsNull){
                if($indexKeyIsNumber){
                    $key        = array_slice($row, $indexKey, 1);
                    $key        = (is_array($key) && !empty($key)) ? current($key) : null;
                    $key        = is_null($key) ? 0 : $key;
                }else{
                    $key        = isset($row[$indexKey]) ? $row[$indexKey] : 0;
                }
            }
            $result[$key]       = $tmp;
        }
        return $result;
    }
}

// 使用例子
$records = array(
    array(
        'id' => 2135,
        'first_name' => 'John',
        'last_name' => 'Doe'
    ),
    array(
        'id' => 3245,
        'first_name' => 'Sally',
        'last_name' => 'Smith'
    ),
    array(
        'id' => 5342,
        'first_name' => 'Jane',
        'last_name' => 'Jones'
    ),
    array(
        'id' => 5623,
        'first_name' => 'Peter',
        'last_name' => 'Doe'
    )
);
$firstNames = array_column($records, 'first_name');
print_r($firstNames);
/*
Array
(
    [0] => John
    [1] => Sally
    [2] => Jane
    [3] => Peter
)
*/

$records = array(
    array(1, 'John', 'Doe'),
    array(2, 'Sally', 'Smith'),
    array(3, 'Jane', 'Jones')
);
$lastNames = array_column($records, 2);
print_r($lastNames);
/*
Array
(
    [0] => Doe
    [1] => Smith
    [2] => Jones
)
*/

$mismatchedColumns = array(
    array(
        'a' => 'foo',
        'b' => 'bar',
        'e' => 'baz'
    ),
    array(
        'a' => 'qux',
        'c' => 'quux',
        'd' => 'corge'
    ),
    array(
        'a' => 'grault',
        'b' => 'garply',
        'e' => 'waldo'
    ),
);
$foo = array_column($mismatchedColumns, 'a', 'b');
print_r($foo);
/*
Array
(
    [bar] => foo
    [0] => qux
    [garply] => grault
)
*/