How to add a value to an array it the key doesn't exist

Question

I want to do something like this:

foreach($values as $key => $value){
    //modify the key here, so it could be the same as one before

    //group by key and accumulate values
    $data[$key]['total'] += $value - $someothervalue;
}

Is this possible in php? or do i have to check this always first?

isset($data[$key]['total'])

You can check if $data[$key] is exist. If not - simply add it. `if (!array_key_exists($key, $data))$data[$key] = [];` or `... = array();` — Michael, Aug 19 '16 at 13:27
If `total` is not exist you can do the same thing but set this field to 0 — Michael, Aug 19 '16 at 13:28

score 1 · Answer 1 · answered Aug 19 '16 at 13:43

If i understand correctly, Can you do it without to check if key exists only in PHP 7 and above

foreach($values as $key => $value)
    $data[$key]['total'] = ($data[$key]['total'] ?? 0) + $value - $someothervalue;;

anyway php allows you to to create new keys like that, but do not forget to disable error reproting in your server to avoid from notices...

Geo Halkiadakis · Answer 2 · 2016-08-19T13:46:02.793

0

Php allows adding a NULL value to a number (when used on numeric operations +,-,* handles it as 0), so you do not need to check isset($data[$key]['total']) if you do not mind overwriting it (and from the += operator I think you do not mind).

edited Aug 19 '16 at 13:46

answered Aug 19 '16 at 13:40

Geo Halkiadakis

370
1
7

score 0 · Answer 3 · edited May 23 '17 at 12:08

You can increment a nonexistent key with +=. If it does not exist, PHP will automatically create it, with an initial value of null, which will be cast to zero when you try to add to it. This will generate two notices each time it occurs:

Notice: Undefined offset: x

where x is the value of $key and

Notice: Undefined index: total

If you don't care about the notices, go ahead. It will work. If you do care about the notices, you have to check if the key exists before you do anything with it. As you said isset($data[$key]['total']) will work for this, but really you only need to check isset($data[$key]) since you're only writing to 'total' for each $key.

foreach($values as $key => $value){
    //modify the key here, so it could be the same as one before

    //group by key and accumulate values
    $inc = $value - $someothervalue;
    if (isset($data[$key])) {
        $data[$key]['total'] += $inc;
    } else {
        $data[$key]['total'] = $inc;
    }
}

I would suggest doing it this way because I do care about notices. There are various other questions that discuss this. They're older and probably would be closed as opinion-based by current standards, but some of the opinions there may offer some insight to help you with that decision.

score 0 · Accepted Answer · answered Aug 19 '16 at 14:31

Thanks for all the answers. I went with:

foreach($values as $key => $value){
    //modify the key here, so it could be the same as one before

    //group by key and accumulate values
    $inc = $value - $someothervalue;

    if (!isset($data[$key]['total']){
        $data[$key]['total'] = 0;
    }

    $data[$key]['total'] = += $inc;
}

How to add a value to an array it the key doesn't exist

4 Answers4