There should be more elegant solutions, but simplest one I can think of would be this.
// The data you have pasted in the question
$data = [];
$groups = [];
// Go through the entire array $data
foreach($data as $item){
// If the key doesn't exist in the new array yet, add it
if(!array_key_exists($item[1], $groups)){
$groups[$item[1]] = [];
}
// Add the value to the array
$groups[$item[1]][] = $item[0];
}
// Create an array for the data with the structure you requested
$structured = [];
foreach($groups as $group => $values){
// With the array built in the last loop, implode it with a comma
// Also add the 'key' from the last array to it ($group)
$structured[] = [implode(',', $values), $group];
}
I haven’t tested this but something similar should do the trick. This simply goes through the given array and collects all entries in a structurized manner (so $groups
variable will contain an array entry for each group sharing a key, and the key will correspond to the 2nd item in each item within the given array). From there it’s just about restructuring it to get the format you have requested.