Arrays & Functional Array Manipulation

In Plain English

PHP arrays are versatile ordered maps that function as lists, stacks, queues, and hash tables. Master short array syntax ([]), associative key-value mapping, array destructuring, and functional array transformers (array_map, array_filter, array_reduce, in_array).

The Mental Model

"A PHP array is like a Swiss Army knife: it acts as a simple sequential list of items, an indexed encyclopedia where words point to definitions, or a nested hierarchy of folders."

Deep Dive: How It Works

Indexed vs Associative: $list = ["apple", "banana"] vs $dict = ["name" => "Alice", "role" => "Admin"].

Array Spread Operator: $combined = [...$arr1, ...$arr2] merges arrays efficiently.

Destructuring: [$first, $second] = $arr or ["name" => $userName] = $data.

Functional Helpers: array_map() transforms values, array_filter() removes falsy items, array_reduce() accumulates a single aggregate.

Syntax Blueprint

<?php

$evens = array_filter($nums, fn($n) => $n % 2 === 0);
$names = array_column($users, "name");
$hasKey = array_key_exists("id", $record);

Transform collections with functional array functions and extract nested columns with array_column.

Core Rules to Remember

Ordered Hash Map: PHP arrays preserve insertion order for both indexed and string-keyed elements.

Array Functions Suite: PHP includes over 80 built-in array functions for sorting, searching, and transforming data.

Spread Unpacking: Use ... to unpack arrays into function calls or merge arrays with precedence.

Common Beginner Traps & How to Fix Them

Mistake:array_filter preserves original integer indices by default, which serializes to JSON as an object instead of an array.

Why it happens: array_filter retains keys 0, 2, 4 if elements 1 and 3 are removed.

How to fix: Wrap result in array_values($filtered) to re-index the array from 0.

Pro Tip: Use array_key_exists() when checking if a key exists with a null value, whereas isset() returns false for null values.

Live Interactive Example

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Functional Pipeline: Filter, Map and Sum

PHP 8.2 / CLI

Output Console

Click "Run Code" to view the rendered output.

How it works: Filtered down to 2 in-stock items ($100 + $250) and computed exact sum of 350.

Your Turn: Micro Challenge

No pressure! Edit the starter code below and test your solution with instant feedback.

Micro Exercise

Double and Filter Numbers

Declare $nums = [5, 12, 8, 20, 3].
Filter numbers that are greater than 6.
Multiply each remaining number by 2 using array_map.
Print the resulting comma-separated list using implode(", ", $result).

Sandbox Output

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