How return is working from array_map PHP

Question

I'm fairly new to PHP, but I understand once PHP hits a return in a function, it will exit out of the function and return to where it was called.

I am confused to how or why in the function below array_map() starts with return and has another inside the function.

function array_plucked($toPluck, $arr) {
return array_map(function($item) use($toPluck) {
    return $item[$toPluck];
}, $arr); }

Also each time it loops through the array what exactly happening to $item[$toPluck], and where is the result being stored?

Will · Accepted Answer · 2016-05-21T09:09:36.257

Good question! Okay, let's clean this up a bit:

function array_pluck($key, $array)
{
    return array_map(function ($item) use ($key) {
        return $item[$key];
    }, $array);
}

It's a bit easier to understand this way.

First, the goal of this function is to return a one-dimensional array of the values of a specific key from a multidimensional array. Here are examples:

$testArray = array(
    array("xxx" => "hello", "yyy" => "goodbye"),
    array("xxx" => "hi", "yyy" => "bye"),
    array("xxx" => "hey", "yyy" => "peace"),
);

php > var_dump(array_pluck('xxx', $testArray));
array(3) {
  [0]=>
  string(5) "hello"
  [1]=>
  string(2) "hi"
  [2]=>
  string(3) "hey"
}

php > var_dump(array_pluck('yyy', $testArray));
array(3) {
  [0]=>
  string(7) "goodbye"
  [1]=>
  string(3) "bye"
  [2]=>
  string(5) "peace"
}
php >

As you can see, this is returning $testArray[<index>]['xxx'] and $testArray[<index>]['yyy'] respectively, for each array inside the parent array.

Now to explain what's going on with the return. The array_map() function takes a function (or "Callable") as the first parameter, and an array as the second parameter. The function is run for each element in the array, and then array_map() adds the return value of that function to the new array that array_map() returns.

This is called an anonymous function:

function ($item) use ($key) {
    return $item[$key];
}

It is just like any other function, except it doesn't have a name, and it does have the use (...) syntax. The use ($key) means to "import" $key from the outer function (array_pluck()), so it can be used inside this anonymous function. Each element of $testArray in the example above, gets passed to this anonymous function as $item. When return $item[$key] occurs, only the anonymous function returns (exits), and the array_map() continues on to the next element.

Good answer, but: "then array_map() replaces the original element with the return value of that function, in the new array that array_map() returns" - it's not clear whether the original array is replaced or a new array is created. I would write something like: "then array_map() adds the return value of that function to the new array that array_map() returns". — Paul Spiegel, May 21 '16 at 08:18
Thanks! I have used your edit. That does sound much more clear. — Will, May 21 '16 at 09:10
No problem @programming2music, glad to help! If your question is completely answered, click the checkbox next to the answer to accept it. — Will, May 21 '16 at 09:10

How return is working from array_map PHP

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