php 38 lines · 6 steps

Grouping records with array_reduce in PHP

A small Collection helper folds flat record arrays into keyed buckets using array_reduce.

Explained by highlit
Intermediate array-reduce grouping higher-order-functions closures static-methods
1<?php
2 
3namespace App\Support;
4 
5final class Collection
6{
7 public static function groupBy(array $records, string $key): array
8 {
9 return array_reduce(
10 $records,
11 static function (array $groups, array $record) use ($key): array {
12 $bucket = $record[$key] ?? '__null__';
13 $groups[$bucket][] = $record;
14 
15 return $groups;
16 },
17 []
18 );
19 }
20 
21 public static function groupByCallback(array $records, callable $resolver): array
22 {
23 return array_reduce(
24 $records,
25 static function (array $groups, $record) use ($resolver): array {
26 $groups[$resolver($record)][] = $record;
27 
28 return $groups;
29 },
30 []
31 );
32 }
33 
34 public static function countByStatus(array $orders): array
35 {
36 return array_map('count', self::groupBy($orders, 'status'));
37 }
38}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1array_reduce with an array accumulator turns a flat list into a keyed structure in one pass.
  2. 2Accepting a callable resolver makes the same fold reusable for any grouping rule.
  3. 3Composing small helpers like groupBy lets aggregates like counts be expressed declaratively.

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