How to convert an array of arrays or objects to an associative array?

Question

I\'m used to perl\'s map() function where the callback can assign both the key and the value, thus creating an associative array where the input was a flat array. I\'m aware of

Answer 1

A good use case of yield operator!

$arr = array('a','b','c','d');

$fct = function(array $items) {
            foreach($items as $letter)
            {
                yield sprintf("key-%s",
                    $letter
                ) => "yes";
            }
        };

$newArr = iterator_to_array($fct($arr));

which gives:

array(4) {
  'key-a' =>
  string(3) "yes"
  'key-b' =>
  string(3) "yes"
  'key-c' =>
  string(3) "yes"
  'key-d' =>
  string(3) "yes"
}

Answer 2

This is a clarification on my comment in the accepted method. Hopefully easier to read. This is from a WordPress class, thus the $wpdb reference to write data:

class SLPlus_Locations {
    private $dbFields = array('name','address','city');

    public function MakePersistent() {
        global $wpdb;
        $dataArray = array_reduce($this->dbFields,array($this,'mapPropertyToField'));
        $wpdb->insert('wp_store_locator',$dataArray);
    }

    private function mapPropertyToField($result,$property) {
        $result[$property] = $this->$property;
        return $result;
    }
}

Obviously there is a bit more to the complete solution, but the parts relevant to array_reduce() are present. Easier to read and more elegant than a foreach or forcing the issue through array_map() plus a custom insert statement.

Nice!

Answer 3

I had the exact same problem some days ago. It is not possible using array_map, but array_reduce does the trick.

$arr = array('a','b','c','d');
$assoc_arr = array_reduce($arr, function ($result, $item) {
    $result[$item] = (($item == 'a') || ($item == 'c')) ? 'yes' : 'no';
    return $result;
}, array());
var_dump($assoc_arr);

result:

array(4) { ["a"]=> string(3) "yes" ["b"]=> string(2) "no" ["c"]=> string(3) "yes" ["d"]=> string(2) "no" }

Answer 4

As far as I know, it is completely impossible in one expression, so you may as well use a foreach loop, à la

$new_hash = array();

foreach($original_array as $item) {
    $new_hash[$item] = 'something';
}

If you need it in one expression, go ahead and make a function:

function array_map_keys($callback, $array) {
    $result = array();

    foreach($array as $item) {
        $r = $callback($item);

        $result[$r[0]] = $r[1];
    }

    return $result;
}