I need a counter within a counter - php

Question

I have searched for this, can't find it and it should be simple, but now I'm crosseyed. Forgive me - I've only been at this for a few months.
I need a counter within a counter in php, such that I pair $Id1 with $Id2, then $Id3, then $Id4, etc. for a single loop through, and then for the second loop pair $Id2 with $Id3, then $Id4, then $Id5 etc. I get the Ids from a sql query, then I use both of them to run a calculation of their relationship, but first I just need the structure to run these two loops, one within the other. Thanks for any help and your patience.
Edited to add what I have so far:
$collection = [];
$sql = 'SELECT id, name FROM table';
$result = mysql_query($sql);
while($row = mysql_fetch_assoc($result))
{
$collection[] = $row;
}
$ct = count($collection);
for ($i = 0; $i < $ct; $i++)
{
$Id1 = $collection[$i]['id'];
for ($j = 0; $j < $ct; $j++)
{
$Id2 = $collection[$j]['id'];
if($Id1 != $Id2){
echo 'IDs: ' . $Id1 . ' ' . $Id2 . '<br>';
}
}
}
}

Answer 1

If you fetch the IDs from your query into an array like this: $ids = [1,2,3,4,5,6,7,8];, you can get a list of pairs using array_chunk, then shifting off the first element, and repeating this process until the array is empty.
while ($ids) { // repeat until empty
$pairs = array_chunk($ids, 2); // split into pairs
foreach ($pairs as $pair) {
if (count($pair) == 2) { // verify that you have a pair (last element will
// have only one item when count($ids) is odd)
var_dump($pair); // do something with your pair of IDs
}
}
$remove_first = array_shift($ids); // shift off the first ID
}
Please note that using array_shift like this will destroy your input array, so if you need to do something else with it as well, make a copy of it before using this approach.