15. PHP Arrays

What you will learn

• How to create indexed arrays
• How to read, add, and remove items
• How to sort and search
• Useful array functions

What is an array?

An array stores several values in one variable. An indexed array uses numbers as positions, starting at 0.

<?php
$courses = ["HTML", "CSS", "JavaScript"];

echo $courses[0] . "<br>";
echo "Count: " . count($courses) . "<br>";
echo "Last: " . $courses[count($courses) - 1];

Changing, adding, and removing

<?php
$list = ["b", "c"];
$list[] = "d";
array_unshift($list, "a");
$last = array_pop($list);

echo implode(", ", $list) . " | popped: " . $last;

Printing an array

You cannot echo a whole array. Use implode() to make text, or print_r() and var_dump() while debugging.

Searching

<?php
$colors = ["red", "green", "blue"];

var_dump(in_array("green", $colors, true));
var_dump(array_search("blue", $colors, true));
var_dump(array_search("pink", $colors, true));

bool(true)
int(2)
bool(false)

Pass true as the last argument for strict comparison. array_search() returns false when nothing is found, and can return 0 for a match at the start, so test it with !== false.

Sorting

<?php
$nums = [10, 9, 100, 1];
sort($nums);
echo implode(", ", $nums) . "<br>";

rsort($nums);
echo implode(", ", $nums);

These functions change the original array. PHP sorts numbers as numbers, unlike JavaScript’s default.

Useful array functions

<?php
$nums = [3, 8, 2, 8, 5];

echo array_sum($nums) . "<br>";
echo implode(",", array_unique($nums)) . "<br>";
echo implode(",", array_reverse($nums)) . "<br>";
echo implode(",", array_slice($nums, 1, 3)) . "<br>";
echo implode(",", array_filter($nums, fn($n) => $n > 4)) . "<br>";
echo implode(",", array_merge([1, 2], [3, 4]));

• array_sum adds the values, and array_unique removes duplicates.
• array_slice($a, start, length) copies part of an array.
• array_filter keeps items that pass a test, and array_merge joins arrays.

Arrays of arrays

An item can itself be an array, making a table of data.

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

echo $grid[1][2];

Row 1, column 2 (counting from 0) is the value 6.

Common mistakes

• Counting from 1. The first item is at index 0.
• Trying to echo an array, which prints the word “Array” with a warning.
• Reading an index that does not exist.
• Forgetting that unset() leaves a gap in the numbers.
• Using array_search() without !== false.

<?php
$todo = ["Wash up", "Study"];
$todo[] = "Exercise";
array_shift($todo);

echo implode(" | ", $todo);

Summary

• Indexed arrays hold lists, with positions starting at 0.
• Use count, implode, in_array, sort, array_filter, and friends.
• Arrays can contain other arrays.