Array mapping in PHP with keys

问题:

Just for curiosity (I know it can be a single line foreach statement), is there some PHP array function (or a combination of many) that given an array like:

Array (
    [0] => stdClass Object (
        [id] => 12
        [name] => Lorem
        [email] => [e-mail]
    )
    [1] => stdClass Object (
        [id] => 34
        [name] => Ipsum
        [email] => [e-mail]
    )
)

And, given 'id' and 'name', produces something like:

Array (
    [12] => Lorem
    [34] => Ipsum
)

I use this pattern a lot, and I noticed that array_map is quite useless in this scenario cause you can't specify keys for returned array.

回答1:

Just use array_reduce:

$obj1 = new stdClass;
$obj1 -> id = 12;
$obj1 -> name = 'Lorem';
$obj1 -> email = '[e-mail]';

$obj2 = new stdClass;
$obj2 -> id = 34;
$obj2 -> name = 'Ipsum';
$obj2 -> email = '[e-mail]';

$reduced = array_reduce(
    // input array
    array($obj1, $obj2),
    // fold function
    function(&$result, $item){ 
        // at each step, push name into $item->id position
        $result[$item->id] = $item->name;
        return $result;
    },
    // initial fold container [optional]
    array()
);

It's a one-liner out of comments ^^

回答2:

I found I can do:

array_combine(array_map(function($o) { return $o->id; }, $objs), array_map(function($o) { return $o->name; }, $objs));

But it's ugly and requires two whole cycles on the same array.

回答3:

Because your array is array of object then you can call (its like a variable of class) try to call with this:

 foreach ($arrays as $object) {
    Echo $object->id;
    Echo "<br>";
    Echo $object->name;
    Echo "<br>";
    Echo $object->email;
    Echo "<br>";
 } 

Then you can do

 // your array of object example $arrays;
 $result = array();
 foreach ($arrays as $array) {
       $result[$array->id] = $array->name;
 }

   echo "<pre>";
   print_r($result);
   echo "</pre>";

Sorry I'm answering on handphone. Can't edit the code

回答4:

The easiest way is to use a LINQ port like YaLinqo library*. It allows performing SQL-like queries on arrays and objects. Its toDictionary function accepts two callbacks: one returning key of the result array, and one returning value. For example:

$userNamesByIds = from($users)->toDictionary(
    function ($u) { return $u->id; },
    function ($u) { return $u->name; }
);

Or you can use a shorter syntax using strings, which is equivalent to the above version:

$userNamesByIds = from($users)->toDictionary('$v->id', '$v->name');

If the second argument is omitted, objects themselves will be used as values in the result array.

_{* developed by me}

回答5:

The easiest way is to use an array_column()

$result_arr = array_column($arr, 'name', 'id');
print_r($result_arr );