PHP Array reference, modifying array values

Question

I'm trying to modify an array when looping through it and increment certain values.

     $data = ['traits' => [[['amt' => 1]]]];
     var_dump($data['traits']);

      foreach ($data['traits'] as $key => &$index) {

        foreach ($index as $key => &$value) {

          $value['amt'] = $value['amt']++; // This should increment

          if (in_array($key, $input)) {
            $i++;
            $insert["field_".$i] = $key."_1";
          }
        }
      }

      var_dump($data['traits']);    // SAME AS PREVIOUS VAR_DUMP

Replace $key in the inner loop by another variable. In your case it gets overwritten and is not what you intended. And do you really want to set $insert in the if clause? Please explain what you are achieving to do. — WeSee
– WeSee, Commented Nov 26, 2014 at 6:12

Ja͢ck · Accepted Answer · 2014-11-26 06:32:17Z

1

What you are doing in the loop is undefined:

$value['amt'] = $value['amt']++;

The outcome of that depends on what's evaluated first. In this case $value['amt']++ seems to be evaluated first and then assigned to $value['amt'] again; the side effect of the increment is lost.

On the other hand, the following statement will work as expected:

$value['amt']++;

edited Nov 26, 2014 at 6:32

answered Nov 26, 2014 at 6:19

Ja͢ck

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