PHP Array Functions Mastery: array_map, filter, reduce and More

Why Array Functions Matter

PHP arrays are ordered maps — the most versatile data structure in PHP. Mastering built-in array functions lets you write clean, readable, interview-worthy code without messy loops.

array_map() — Transform Every Element

<?php
$numbers = [1, 2, 3, 4, 5];

// Double every number
$doubled = array_map(fn($n) => $n * 2, $numbers);
// [2, 4, 6, 8, 10]

// Map with index using array_keys
$indexed = array_map(null, $numbers, array_keys($numbers));

// Real use: format prices
$prices    = [999, 1499, 2999];
$formatted = array_map(fn($p) => '₹' . number_format($p), $prices);
// ['₹999', '₹1,499', '₹2,999']

// Multiple arrays
$a    = [1, 2, 3];
$b    = [10, 20, 30];
$sums = array_map(fn($x, $y) => $x + $y, $a, $b);
// [11, 22, 33]

array_filter() — Keep Matching Elements

<?php
$numbers = [1, 2, 3, 4, 5, 6, 7, 8];

// Keep only even numbers (keys preserved!)
$evens = array_filter($numbers, fn($n) => $n % 2 === 0);
// [1=>2, 3=>4, 5=>6, 7=>8]  ← original indices kept

// Re-index with array_values()
$evens = array_values(array_filter($numbers, fn($n) => $n % 2 === 0));
// [0=>2, 1=>4, 2=>6, 3=>8]

// Filter active users
$users = [
    ['name' => 'Rahul', 'active' => true],
    ['name' => 'Priya', 'active' => false],
    ['name' => 'Amit',  'active' => true],
];
$active = array_values(array_filter($users, fn($u) => $u['active']));
// [Rahul, Amit]

// Without callback — removes falsy values
$cleaned = array_filter([0, 1, '', 'hello', null, false, 42]);
// [1, 'hello', 42]

array_reduce() — Collapse to Single Value

<?php
$numbers = [1, 2, 3, 4, 5];

// Sum (accumulator starts at 0)
$sum = array_reduce($numbers, fn($carry, $item) => $carry + $item, 0);
// 15

// Product
$product = array_reduce($numbers, fn($carry, $item) => $carry * $item, 1);
// 120

// Real use: calculate cart total
$cart = [
    ['name' => 'PHP Book',  'price' => 499, 'qty' => 2],
    ['name' => 'JS Course', 'price' => 999, 'qty' => 1],
];
$total = array_reduce($cart, fn($carry, $item) => $carry + ($item['price'] * $item['qty']), 0);
// 1997

// Build lookup map from array of objects
$users = [['id'=>1,'name'=>'Rahul'],['id'=>2,'name'=>'Priya']];
$map   = array_reduce($users, function($carry, $user) {
    $carry[$user['id']] = $user['name'];
    return $carry;
}, []);
// [1 => 'Rahul', 2 => 'Priya']

Sorting with usort()

<?php
$products = [
    ['name' => 'Laptop', 'price' => 55000],
    ['name' => 'Phone',  'price' => 15000],
    ['name' => 'Tablet', 'price' => 25000],
];

// Sort by price ascending
usort($products, fn($a, $b) => $a['price'] - $b['price']);
// Phone -> Tablet -> Laptop

// Sort by price descending
usort($products, fn($a, $b) => $b['price'] - $a['price']);

// Sort strings case-insensitively
$names = ['Zebra', 'apple', 'Mango', 'banana'];
usort($names, fn($a, $b) => strcasecmp($a, $b));
// apple, banana, Mango, Zebra

Essential Utility Functions

<?php
$arr = [3, 1, 4, 1, 5, 9, 2, 6];

$unique  = array_unique($arr);              // remove duplicates
$flipped = array_flip(['a'=>1,'b'=>2]);     // [1=>'a', 2=>'b']
$merged  = array_merge([1,2], [3,4]);       // [1,2,3,4]
$slice   = array_slice($arr, 2, 3);         // [4,1,5]
$chunks  = array_chunk([1,2,3,4,5], 2);    // [[1,2],[3,4],[5]]
$key     = array_search(5, $arr);           // 4 (index)
$has     = in_array(5, $arr);              // true

// array_column — extract a column from 2D array
$users = [['id'=>1,'name'=>'Rahul'],['id'=>2,'name'=>'Priya']];
$names = array_column($users, 'name');          // ['Rahul','Priya']
$byId  = array_column($users, 'name', 'id');   // [1=>'Rahul', 2=>'Priya']

Real Pipeline Example

<?php
$orders = [
    ['id'=>1,'amount'=>500,'status'=>'paid'],
    ['id'=>2,'amount'=>1200,'status'=>'pending'],
    ['id'=>3,'amount'=>800,'status'=>'paid'],
    ['id'=>4,'amount'=>300,'status'=>'cancelled'],
];

// Total of paid orders only — filter then reduce
$paidTotal = array_reduce(
    array_filter($orders, fn($o) => $o['status'] === 'paid'),
    fn($carry, $o) => $carry + $o['amount'],
    0
);
// 1300 (500 + 800)

// Get names of paid orders — filter then map then column
$paidIds = array_column(
    array_values(array_filter($orders, fn($o) => $o['status'] === 'paid')),
    'id'
);
// [1, 3]