PHP defined function to Flip array keys and values without grouping

Question

Is there any predefined function in any version of PHPs which could do this:

I have this array:

$arr = array(
    2 => 'John',
    21 => 'John',
    32 => 'Joe',
    42 => 'John',
    23 => 'Joe',
    62 => 'John',
    25 => 'Joe',
    );

I expect this result:

array(
    'John' => array(2, 21, 42, 62),
    'Joe' => array(32, 23, 25),
);

array_flip doesn't do what I want.

Note: I can write a custom code to do that and it's easy. My question is if there is a function in PHP can do it?

Last update: I think the answer should be NO

There's nothing do do that with a predefined function, but plenty of array functions that you can use with a custom callback. — cmbuckley, Jun 08 '16 at 16:08
Tried searching in [SO](http://stackoverflow.com/a/12425481/5447994)? — Thamilhan, Jun 08 '16 at 16:43

score 6 · Answer 1 · answered Jun 08 '16 at 16:23

6

This is solved quite simply with a foreach loop

$flipped = [];
foreach($arr AS $key => $value) {
    $flipped[$value][] = $key;
}

No it's not a function. But it's simple, why make it more complicated?

answered Jun 08 '16 at 16:23

jszobody

3

Exactly. This is the best way. – Ryan Jun 08 '16 at 16:26
I was intrigued about that; turns out you don't get an error at all! – cmbuckley Jun 08 '16 at 16:40
1

Because it's assignment. If I was trying to retrieve an array index that doesn't exist, I'd get undefined. Assignment works though. – jszobody Jun 08 '16 at 16:40
@Thamilan yep! except we now have short array syntax, yay. – jszobody Jun 08 '16 at 16:45
@jszobody I never downvote any answer.. I upvoted yours both first. I downvote only questions that are duplicates – Thamilhan Jun 08 '16 at 16:46
I didn't want a custom code. Please delete your answer. I am going to delete this question. tnx. – Mojtaba Jun 08 '16 at 16:46
@Mojtaba you shouldn't delete a question after answers have been received. You showed the result you needed, and two people here helped you get it. – jszobody Jun 08 '16 at 16:48
@Thamilan my bad, was just the timing that made me think that. – jszobody Jun 08 '16 at 16:48
@jszobody the surprising lack of error is that you can essentially do `$foo[] = 1` when `$foo` is undefined. – cmbuckley Jun 08 '16 at 16:49
@jszobody, These 2 people didn't read my request carefully. It was easy for me to use a loop to create that. I asked in my question I am looking for a PHP function. Not a custom code. – Mojtaba Jun 08 '16 at 16:50
1

If you just wanted the answer yes or no, couldn't you have read the documentation to determine that? – cmbuckley Jun 08 '16 at 16:52

cmbuckley · Answer 2 · 2016-06-08T16:26:12.723

4

You could do this with array_reduce:

$flipped = array_reduce(array_keys($arr), function ($carry, $item) use ($arr) {   
    $carry[$arr[$item]][] = $item;
    return $carry;
}, array());

edited Jun 08 '16 at 16:26

answered Jun 08 '16 at 16:14

cmbuckley

I didn't want a custom code. Please delete your answer. I am going to delete this question. tnx. – Mojtaba Jun 08 '16 at 16:46
2

@Mojtaba to be fair, this answer is using a predefined function to do exactly what you want. even if I think a loop is simpler, this answer is technically what you asked for. you should probably accept it. – jszobody Jun 08 '16 at 16:52
@jszobody, Thanks. However, it's a custom code with a closure function. – Mojtaba Jun 08 '16 at 16:57

2 Answers2