根据组为值分配键

Question

Values of array are grouped together if they have the same $record->parent_id. How can I assign to each group a key that starts from 0 and iterates for every member of a group and only for that specific group? Every consecutive new group starts from 0 again.

Example: if $record->parent_id is 2, current iteration of foreach loop assigns a 0 to key. Next iteration has $record->parent_id of value 56, its key is 0 again! Next iteration has $record->parent_id of value 2 again, hence its key is now 1 and so forth.

My current code:

<?php foreach ($records as $key => $record): ?>   

<tr id="<?php echo $key; ?>">
    <td><?php echo $record->parent_id; ?></td>
    <td><?php echo $key; ?></td> //here I wish to get key starting from 0
    <td><?php echo $record->title; ?></td>
</tr>     

<?php endforeach; ?>

Answer 1

First of all I notice that your current code introduces an ambiguity, since it uses $key twice for different things.

If I correctly understand what's your need:

• $key in 1st and 2nd lines is some existing key you get from each record and which must become the id of the corresponding generated <tr>.
  To emphasize it I will change its name below to $record_key
• $key in ghe 4th line is a count number within the group of all records having the same parent_id.
  This can be achieved by merely counting rows in their relevant group.

Here is the result:

foreach ($records as $record_key => $record) {
  if (!isset($groups[$record->parent_id]) {
    $groups[$record->parent_id] = 0;
  }
?>   
<tr id="<?php echo $record_key; ?>">
    <td><?php echo $record->parent_id; ?></td>
    <td><?php echo $groups[$record->parent_id]++; ?></td>
    <td><?php echo $record->title; ?></td>
</tr>     
<?php
}