Laravel 5 Collections: Transforming Collection Element Keys With keyBy

The keyBy method is used to create a new Collection instance where the keys of the new key/value pairs are determined by a $keyBy callback function (a string value can also be supplied instead of a function). The signature of the callback function is keyBy($item), where the $item is the actual item in the collection. This method does not change the original Collection instance will will return a new, modified, Collection instance.

#Signature

1public function keyBy(
2    $keyBy
3);

#Example Use

The following sample will be used to demonstrate the keyBy method:

1// Create a new collection.
2$people = collect([
3    ['id' => 12, 'name' => 'Alice', 'age' => 26],
4    ['id' => 52, 'name' => 'Bob',   'age' => 34],
5    ['id' => 14, 'name' => 'Chris', 'age' => 26]
6]);

In the following example, we will create a new collection instance where the key of each item is the persons id. We will not supply a callback function in this example, but rather pass the name of the value we want to use as the key as as string:

1$results = $people->keyBy('id');

After the above code has executed, the $results variable will contain a value similar to the following output:

 1Collection {
 2  #items: array [
 3    12 => array [
 4      "id"   => 12
 5      "name" => "Alice"
 6      "age"  => 26
 7    ]
 8    52 => array [
 9      "id"   => 52
10      "name" => "Bob"
11      "age"  => 34
12    ]
13    14 => array [
14      "id"   => 14
15      "name" => "Chris"
16      "age"  => 26
17    ]
18  ]
19}

We can also achieve the exact same results by using a callback function like so:

1$results = $people->keyBy(function($item) {
2    return $item['id'];
3});

However, the above example is overly complicated if all we were interested in was just the id of the person. We could do something a little more interesting, such as returning a simple hash of each persons id to use as the new key:

1$results = $people->keyBy(function($item) {
2    return md5($item['id']);
3});

After the above code has executed, the new $results variable would contain a value similar to the following output:

 1Collection {
 2  #items: array [
 3    "c20ad4d76fe97759aa27a0c99bff6710" => array [
 4      "id"   => 12
 5      "name" => "Alice"
 6      "age"  => 26
 7    ]
 8    "9a1158154dfa42caddbd0694a4e9bdc8" => array [
 9      "id"   => 52
10      "name" => "Bob"
11      "age"  => 34
12    ]
13    "aab3238922bcc25a6f606eb525ffdc56" => array [
14      "id"   => 14
15      "name" => "Chris"
16      "age"  => 26
17    ]
18  ]
19}

The same method could just as easily be applied to other hashing libraries, such as the hashids.php library.

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