Array functions

Many array tasks repeat: transform every element, pick the matching ones, compute a total. PHP has ready-made functions for them — code that uses them is shorter than a loop and shows at once what it does.

array_map

array_map() applies a function to every element and returns a new array:

<?php
 
$prices = [100, 250, 400];
 
$withTax = array_map(fn ($price) => $price * 1.2, $prices);
 
echo implode(', ', $withTax); // 120, 300, 480

The function comes first, the array second.

array_filter

array_filter() keeps the elements for which the function returned true:

<?php
 
$numbers = [5, 12, 8, 20];
 
$big = array_filter($numbers, fn ($number) => $number > 10);
 
echo implode(', ', $big); // 12, 20

Here the argument order is reversed: the array first, then the function.

array_reduce

array_reduce() reduces an array to a single value. The function receives the accumulated result and the next element:

<?php
 
$cart = [100, 250, 400];
 
$total = array_reduce($cart, fn ($sum, $price) => $sum + $price, 0);
 
echo $total; // 750

The third argument is the initial value. For a plain sum there is the ready-made array_sum().

A chain of transformations

Functions can be combined: the result of one goes into another:

<?php
 
$orders = [
    ['total' => 500, 'paid' => true],
    ['total' => 300, 'paid' => false],
    ['total' => 200, 'paid' => true],
];
 
$paid = array_filter($orders, fn ($order) => $order['paid']);
$totals = array_column($paid, 'total');
 
echo array_sum($totals); // 700

array_column() pulls the values of one key out of an array of arrays.

Searching

<?php
 
$fruits = ['apple', 'pear', 'plum'];
 
var_dump(in_array('pear', $fruits));  // bool(true)
echo array_search('plum', $fruits);   // 2

in_array() tells whether a value is present, and array_search() returns its key or false.

Parts of an array

<?php
 
$numbers = [1, 2, 3, 4, 5];
 
echo implode(', ', array_slice($numbers, 1, 3)), "\n";   // 2, 3, 4
echo implode(', ', array_merge([1, 2], [3, 4])), "\n";   // 1, 2, 3, 4
echo implode(', ', array_unique([1, 2, 2, 3, 1])), "\n"; // 1, 2, 3
echo implode(', ', array_reverse($numbers));             // 5, 4, 3, 2, 1

All these functions return a new array and leave the original untouched.

Common mistake

array_filter() keeps the original keys, so the result has "gaps" in its numbering. Accessing index 0 may not work:

<?php
 
$numbers = [5, 12, 8, 20];
$big = array_filter($numbers, fn ($number) => $number > 10);
 
echo implode(', ', array_keys($big)), "\n"; // 1, 3
 
$big = array_values($big);
 
echo $big[0]; // 12

array_values() renumbers the array from zero.

Thanks for reading!