Sort array in groups and people with foreach - php

Question

I am trying to sort an array into groups and people.
the problem is that it only shows me one person per class when I use the counter "pos_group = 0" but if I put it in negative and increase it in the "IF" if I get the result.
Am I doing something else in the assignment of the new array?
<?php
$data = [
0 => [
'g_id' => 22,
'g_name' => 'ABC',
'u_id' => 1,
'u_name'=> 'Pepe'
],
1 => [
'g_id' => 22,
'g_name' => 'ABC',
'u_id' => 2,
'u_name'=> 'Mario'
],
2 => [
'g_id' => 22,
'g_name' => 'ABC',
'u_id' => null,
'u_name'=> null
],
3 => [
'g_id' => 31,
'g_name' => 'CDE',
'u_id' => 3,
'u_name'=> 'Juan'
],
4 => [
'g_id' => 41,
'g_name' => 'EFG',
'u_id' => 4,
'u_name'=> 'Pedro'
],
];
$last_group_id = null;
$pos_group = 0;
foreach ($data as $group_user):
//Add Groups
if($last_group_id != $group_user['g_id']){
//$pos_group ++;
$final[$pos_group] = [
'g_id' => $group_user['g_id'],
'g_name' => $group_user['g_name']
];
//$last_group_id = $group_user['g_id'];
//$pos_group ++;
}
//Add Members
if(!is_null($group_user['u_id'])){
$final[$pos_group]['members'][$group_user['u_id']] = [
'u_id' => $group_user['u_id'],
'u_name' => $group_user['u_name']
];
}
if($last_group_id != $group_user['g_id']){
$pos_group ++;
$last_group_id = $group_user['g_id'];
}
endforeach;
echo "<pre>";
print_r($final);
//var_dump($final);
echo "</pre>";
?>
expected:
Array
(
[0] => Array
(
[g_id] => 22
[g_name] => ABC
[members] => Array
(
[1] => Array
(
[u_id] => 1
[u_name] => Pepe
)
[2] => Array
(
[u_id] => 2
[u_name] => Mario
)
)
)
[1] => Array
(
[g_id] => 31
[g_name] => CDE
[members] => Array
(
[3] => Array
(
[u_id] => 3
[u_name] => Juan
)
)
)
[2] => Array
(
[g_id] => 41
[g_name] => EFG
[members] => Array
(
[4] => Array
(
[u_id] => 4
[u_name] => Pedro
)
)
)
)
I only get that result by setting the variable to -1 and increasing the counter after the "if", like this:
$last_group_id = null;
$pos_group = -1;
foreach ($data as $group_user):
//Add Groups
if($last_group_id != $group_user['g_id']){
$pos_group ++;
$final[$pos_group] = [
'g_id' => $group_user['g_id'],
'g_name' => $group_user['g_name']
];
$last_group_id = $group_user['g_id'];
//$pos_group ++;
}
//Add Members
if(!is_null($group_user['u_id'])){
$final[$pos_group]['members'][$group_user['u_id']] = [
'u_id' => $group_user['u_id'],
'u_name' => $group_user['u_name']
];
}
// if($last_group_id != $group_user['g_id']){
// $pos_group ++;
// $last_group_id = $group_user['g_id'];
// }
endforeach;
It's a bit silly but I can't find the problem XD
thanks !

Answer 1

It has to do with the position of your counter increment. The first case increments at the end of the loop, while the second one does it early in the loop. Let's observe what happens in the first case (incrementing at the end):
first iteration
$pos_group is 0
a new group is added (with id 22) at index 0
a new member is added inside that group (Pepe)
$pos_group is incremented to 1
second iteration
$pos_group is 1
group is not added as it is the same as the previous one
a new member is added (Mario), but at index 1, which places it outside the group (because the first member was added while $pos_group was 0)
$pos_group is not incremented
third iteration
here no changes are made, group is the same and id is null
fourth iteration
$pos_group is still 1 (no increment in last two iterations)
a new group is added at index 1, overwriting poor Mario
...algorithm continues normally until the end...
So the discrepancy happens because the first two members of the group are added at different indices. Incrementing the $pos_group variable at the beginning, before any additions, removes the problem, thus giving correct result.
But I'd like to suggest a simplified algorithm for this purpose:
$final = [];
foreach ($data as $groupUser) {
if (null !== $groupUser['u_id']) {
/* Note that for the final array I use the group id as key. That way
instead of tracking the current position and last group, you can simply
add at the group id index. I am also overwriting the group info every time
instead of checking if it exists (for simplicity), becuase there is no harm
done since it will always be the same. */
$final[$groupUser['g_id']]['g_id'] = $groupUser['g_id'];
$final[$groupUser['g_id']]['g_name'] = $groupUser['g_name'];
// add member, we've already checked the id against null
$final[$groupUser['g_id']]['members'][$groupUser['u_id']] = [
'u_id' => $groupUser['u_id'],
'u_name' => $groupUser['u_name']
];
}
}
No multiple checks, no additional variables to track, with the added benefit of working on unsorted data as well. The only difference is that my solution will have top level keys equal to group ids:
Array
(
[22] => Array...
[31] => Array...
If this is in any way a problem for you, all you have to do is grab array_values($final) to get a reindexed array, starting at 0.