Arrays

The array is PHP's workhorse. A single type serves as a list, a dictionary, a stack, a queue and a table of rows from a database. This lesson starts with indexed arrays — ordered lists numbered from 0 — and how to create, read, change, count and loop over them.

Creating an array

Write the values in square brackets, separated by commas. Each element gets a numeric key (an index) starting at 0:

PHP 
<?php

$fruits = ["apple", "banana", "cherry"];
$scores = [72, 95, 88];
$empty = [];
$mixed = [1, "two", 3.0, true];    // any types can be mixed

echo $fruits[0], "\n";
echo $scores[2], "\n";
echo count($fruits), "\n";
var_dump($empty === []);
print_r($mixed);
Output
apple
88
3
bool(true)
Array
(
    [0] => 1
    [1] => two
    [2] => 3
    [3] => 1
)

The older syntax array("apple", "banana") does the same thing; you'll see it in older code.

Reading and changing elements

PHP 
<?php

$seats = ["Ana", "Ben", "Chen", "Dara"];

echo $seats[1], "\n";
echo $seats[count($seats) - 1], "\n";

$seats[1] = "Bilal";          // replace
$seats[] = "Eli";             // append to the end
echo implode(", ", $seats), "\n";
echo count($seats), "\n";
Output
Ben
Dara
Ana, Bilal, Chen, Dara, Eli
5

$array[] = value appends — you'll use it constantly to build arrays in loops. Unlike strings, arrays don't support negative indexes like $seats[-1]; to get the last element, use array_last() (PHP 8.5) or end().

Missing elements

Reading an index that doesn't exist gives a warning and null. Check with isset or array_key_exists, or use ?? for a default:

PHP 
<?php

$colours = ["red", "green"];

echo $colours[5] ?? "(none)", "\n";
var_dump(isset($colours[1]), isset($colours[5]));
echo $colours[5];
Output
(none)
bool(true)
bool(false)

Warning: Undefined array key 5 in main.php on line 7

Building arrays in loops

PHP 
<?php

$squares = [];
for ($i = 1; $i <= 5; $i++) {
    $squares[] = $i * $i;
}
echo implode(" ", $squares), "\n";

$long = [];
foreach (["kiwi", "banana", "fig", "cherry"] as $fruit) {
    if (strlen($fruit) > 4) {
        $long[] = $fruit;
    }
}
echo implode(", ", $long), "\n";
Output
1 4 9 16 25
banana, cherry

Lesson 23 shows array_map and array_filter, which do the same jobs in one line.

Adding and removing at the ends

Four functions treat an array like a stack or a queue:

PHP 
<?php

$queue = ["b", "c"];

array_push($queue, "d", "e");     // add to the end
array_unshift($queue, "a");       // add to the start
echo implode(" ", $queue), "\n";

$last = array_pop($queue);        // remove from the end
$first = array_shift($queue);     // remove from the start
echo "removed $first and $last: ", implode(" ", $queue), "\n";
Output
a b c d e
removed a and e: b c d

Removing from the middle

unset removes an element but leaves a gap in the keys. array_values renumbers them; array_splice removes and renumbers in one go:

PHP 
<?php

$letters = ["a", "b", "c", "d"];
unset($letters[1]);
print_r($letters);
print_r(array_values($letters));

$nums = [10, 20, 30, 40, 50];
array_splice($nums, 1, 2);                 // remove 2 elements from index 1
echo implode(" ", $nums), "\n";
array_splice($nums, 1, 0, [15, 18]);       // insert without removing
echo implode(" ", $nums), "\n";
Output
Array
(
    [0] => a
    [2] => c
    [3] => d
)
Array
(
    [0] => a
    [1] => c
    [2] => d
)
10 40 50
10 15 18 40 50

Searching

PHP 
<?php

$temps = [18, 22, 25, 19, 30, 22];

var_dump(in_array(25, $temps, true));
var_dump(array_search(22, $temps, true));    // first matching key
var_dump(array_search(99, $temps, true));
echo max($temps), " ", min($temps), " ", array_sum($temps) / count($temps), "\n";
echo array_first($temps), " ", array_last($temps), "\n";
Output
bool(true)
int(1)
bool(false)
30 18 22.666666666667
18 22

Pass true as the third argument to in_array and array_search for strict comparison. And as with strpos, array_search can return key 0, so compare its result with !== false. array_first and array_last are new in PHP 8.5.

Slicing and combining

PHP 
<?php

$months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun"];

echo implode(" ", array_slice($months, 2, 3)), "\n";
echo implode(" ", array_slice($months, -2)), "\n";

$more = ["Jul", "Aug"];
echo implode(" ", array_merge($months, $more)), "\n";
echo implode(" ", [...$months, ...$more]), "\n";      // spread (lesson 26)
echo implode(" ", array_reverse($more)), "\n";
Output
Mar Apr May
May Jun
Jan Feb Mar Apr May Jun Jul Aug
Jan Feb Mar Apr May Jun Jul Aug
Aug Jul

Arrays are copied on assignment

Assigning an array to another variable, or passing it to a function, gives an independent copy. (PHP is clever about this: it only actually copies when one of them is modified.)

PHP 
<?php

$original = [1, 2, 3];
$copy = $original;
$copy[0] = 100;

echo implode(",", $original), " / ", implode(",", $copy), "\n";

function addItem(array $list): array
{
    $list[] = "new";
    return $list;
}

$items = ["a"];
$result = addItem($items);
echo count($items), " vs ", count($result), "\n";
Output
1,2,3 / 100,2,3
1 vs 2

Try it yourself

Find the hottest and coldest days of the week and the average temperature.

Try it yourself · main.php
Edit the code, copy it into main.php, then run it with php main.php (PHP 8.5). How to install PHP
Output
Hottest: Sun (23.1 °C)
Coldest: Fri (16.5 °C)
Average: 19.8 °C
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