Group a given input array using a configurable set of fields.

group-array.php

<?php

/**
 * Given a 2-dimensional array, this function returns a mapped 2-dimensional
 * array wherein the rows of the input array have been 'grouped'.
 * 
 * 'Grouping' involves merging similar rows of the input array. Rows are
 * considered 'similar' if some subset of their fields are found to be
 * equivalent to each other. This subset of fields is identified using the
 * '$group_by' argument. 'Merging' involves the creation of an array of the
 * values of similar rows, wherein this array of similar rows is substituted in
 * as the value of the field from which the array was created for the 'grouped'
 * row. The fields that will be merged can be decided using the '$group_into'
 * argument.
 * 
 * @param array $input The input 2-dimensional array to group.
 * @param array $group_by The fields that will be used to decide if two rows
 * should be merged.
 * @param array $group_into The fields that will be merged for rows determined
 * to be 'similar'.
 * @return array The resulting grouped array.
 */
function groupArray(array $input, array $group_by, array $group_into): array {
	
	$results = [];
	$current_item = null;
	$current_group = array_fill(0, count($group_by), "");
	
	foreach ($input as $item) {
		
		$is_item_object = is_object($item);
		
		$item = (array) $item;
		
		$item_group = array_map(
			callback: fn($group_by_field) => $item[$group_by_field],
			array: $group_by,
		);
		
		if ($item_group !== $current_group) {
			
			if (!is_null($current_item)) {
				
				if ($is_item_object) $results[] = (object) $current_item;
				else $results[] = $current_item;
				
			}
			
			$current_group = $item_group;
			$current_item = $item;
			
			foreach ($group_into as $group_into_field) {
				
				$current_item[$group_into_field] = [];
			
			}
			
		}
		
		foreach ($group_into as $group_into_field) {
			
			$current_item[$group_into_field][] = $item[$group_into_field];
			
		}
		
	}
	
	if (!is_null($current_item)) {
		
		if ($is_item_object) $results[] = (object) $current_item;
		else $results[] = $current_item;
		
	}
	
	return $results;
	
}