Create Arrays

There are many ways to create an array in PHP: writing it out literally, generating it with a function, converting it from a string or JSON, or building it step by step in a loop. Choosing the right technique makes code shorter and clearer. This lesson covers each approach and when to use it.

Array Literals

Short Syntax []

<?php
$colors = ['red', 'green', 'blue'];
$user = ['name' => 'Asha', 'city' => 'Chennai'];
$empty = [];
var_dump(count($colors), count($user), count($empty));

Output

int(3)
int(2)
int(0)

• Without keys, values receive automatic integer keys 0, 1, 2, ….
• With key => value, you choose the keys.
• [] creates an empty array, ready to be filled.

Long Syntax array()

$colors = array('red', 'green', 'blue');

array() is a language construct that creates exactly the same array. It was the only syntax before PHP 5.4 and still appears in older code. Use [] in new code.

Multi-line Literals and Trailing Commas

<?php
$config = [
    'app_name' => 'GoCourse',
    'debug' => false,
    'timezone' => 'Asia/Kolkata',
    'supported_languages' => ['en', 'ta', 'hi'],
];
echo $config['supported_languages'][1] . "\n";

Output

ta

A trailing comma after the last element is allowed. It makes adding or reordering lines easier and keeps version-control diffs clean.

Mixing Explicit and Automatic Keys

<?php
$items = [5 => 'five', 'six', 'name' => 'mixed', 'seven'];
print_r($items);

Output

Array
(
    [5] => five
    [6] => six
    [name] => mixed
    [7] => seven
)

When no key is given, PHP uses the largest integer key so far plus one. String keys do not affect this counter. Mixing styles like this is legal but confusing; in practice, an array is usually either a list (automatic keys) or a map (explicit keys).

Duplicate Keys: The Last Value Wins

<?php
$settings = ['theme' => 'light', 'language' => 'en', 'theme' => 'dark'];
print_r($settings);

Output

Array
(
    [theme] => dark
    [language] => en
)

An array cannot contain the same key twice. The later value replaces the earlier one, but the key keeps its original position. Duplicate keys in a literal are usually a typo; static analysis tools report them.

Functions That Create Arrays

Example

<?php
print_r(range(0, 20, 5));
print_r(array_fill(0, 3, 'TBD'));
print_r(array_fill_keys(['name', 'email', 'phone'], ''));
print_r(array_combine(['IN', 'JP'], ['India', 'Japan']));
print_r(array_pad([1, 2], 5, 0));

Output

Array
(
    [0] => 0
    [1] => 5
    [2] => 10
    [3] => 15
    [4] => 20
)
Array
(
    [0] => TBD
    [1] => TBD
    [2] => TBD
)
Array
(
    [name] => 
    [email] => 
    [phone] => 
)
Array
(
    [IN] => India
    [JP] => Japan
)
Array
(
    [0] => 1
    [1] => 2
    [2] => 0
    [3] => 0
    [4] => 0
)

Where Each Is Useful

• range() — page numbers, years for a dropdown, test data.
• array_fill() — placeholders, such as empty slots in a schedule.
• array_fill_keys() — a form's default values, or counters initialized to 0 for known categories.
• array_combine() — pairing two lists (for example, CSV headers with a CSV row). Both arrays must have the same number of elements, or PHP throws a ValueError.
• array_pad() — making rows the same length before building a table.

From Strings

<?php
$csvLine = 'php,mysql,laravel';
$tags = explode(',', $csvLine);
$code = 'AB12CD34';
$chunks = str_split($code, 2);
echo implode(' | ', $tags) . "\n";
echo implode('-', $chunks) . "\n";

Output

php | mysql | laravel
AB-12-CD-34

From Variables: compact()

<?php
$name = 'Asha';
$city = 'Chennai';
$age = 24;
$user = compact('name', 'city', 'age');
print_r($user);

Output

Array
(
    [name] => Asha
    [city] => Chennai
    [age] => 24
)

compact() builds an array whose keys are the variable names. It is common in older templates and some frameworks for passing variables to views. Writing the array explicitly (['name' => $name, ...]) is often clearer, and editors can track it better.

From JSON

<?php
$json = '{"title": "PHP Arrays", "lessons": 16, "topics": ["indexed", "associative"]}';
$course = json_decode($json, true);
echo $course['title'] . ' has ' . $course['lessons'] . " lessons\n";
echo 'First topic: ' . $course['topics'][0] . "\n";

Output

PHP Arrays has 16 lessons
First topic: indexed

The second argument true returns associative arrays instead of objects. Invalid JSON returns null; use the JSON_THROW_ON_ERROR flag to get an exception instead (see PHP JSON).

Building Arrays Dynamically

In a Loop

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

Output

1, 4, 9, 16, 25

Start with an empty array and append with $array[] = .... Initializing $squares = [] first is important: it guarantees the variable is an array even if the loop runs zero times.

With array_map()

<?php
$squares = array_map(fn(int $n): int => $n * $n, range(1, 5));
echo implode(', ', $squares) . "\n";

Output

1, 4, 9, 16, 25

Generating the input with range() and transforming it with array_map() produces the same result in one expression.

By Combining Arrays

<?php
$basics = ['Variables', 'Strings'];
$advanced = ['Closures', 'Generators'];
$syllabus = [...$basics, 'Arrays', ...$advanced];
echo implode(' → ', $syllabus) . "\n";

Output

Variables → Strings → Arrays → Closures → Generators

The spread operator ... copies elements from other arrays into a new array literal. See Array Spread Operator.

From Generators and Iterators

<?php
function evenNumbers(int $limit): Generator
{
    for ($n = 2; $n <= $limit; $n += 2) {
        yield $n;
    }
}
$evens = iterator_to_array(evenNumbers(10));
echo implode(', ', $evens) . "\n";

Output

2, 4, 6, 8, 10

iterator_to_array() collects all values produced by a generator or iterator into an array. Generators are covered in PHP Generators.

Practical Example: An Event Seat Map

<?php
$rows = range('A', 'C');
$seatsPerRow = 4;
$seats = array_fill_keys($rows, array_fill(1, $seatsPerRow, 'free'));
$seats['B'][2] = 'taken';
$seats['C'][4] = 'taken';
foreach ($seats as $row => $rowSeats) {
    $symbols = array_map(fn(string $status): string => $status === 'free' ? '○' : '●', $rowSeats);
    echo $row . ' ' . implode(' ', $symbols) . "\n";
}
$freeCount = 0;
foreach ($seats as $rowSeats) {
    $freeCount += count(array_keys($rowSeats, 'free', true));
}
echo "Free seats: $freeCount\n";

Output

A ○ ○ ○ ○
B ○ ● ○ ○
C ○ ○ ○ ●
Free seats: 10

Step-by-Step Explanation

1. range('A', 'C') creates the row letters ['A', 'B', 'C'].
2. array_fill(1, 4, 'free') creates one row of seats numbered 1 to 4 (seat numbers start at 1, as people expect).
3. array_fill_keys() gives each row letter its own copy of that row, producing a two-level array.
4. Individual seats are updated with two keys: $seats['B'][2].
5. For display, array_map() converts statuses to symbols.
6. array_keys($rowSeats, 'free', true) returns the keys whose value is exactly 'free'; counting them gives the free seats per row. Because arrays are copied on assignment, each row is independent — changing row B does not affect rows A or C.

Common Mistakes

Not Initializing Before Appending

Effect: If a loop never runs, the variable is undefined later; appending to a variable holding false triggers a deprecation notice since PHP 8.1. Fix: Initialize with $items = []; before the loop.

Duplicate Keys in Literals

Effect: Earlier values are silently overwritten. Fix: Check literals carefully; use a static analyzer.

array_combine() With Different Lengths

Effect: ValueError. Fix: Ensure both arrays have the same count (for example, validate CSV rows against headers).

Forgetting true in json_decode()

Effect: You get stdClass objects, and $data['key'] fails. Fix: json_decode($json, true) for arrays.

Best Practices

• Use [] literals with trailing commas for fixed data.
• Use range(), array_fill(), array_fill_keys(), and array_combine() to generate structured arrays instead of manual loops.
• Initialize arrays before building them in loops.
• Keep each array either a list or a map rather than mixing key styles.
• Convert external data (strings, JSON) with the dedicated functions and validate the result. Official reference: https://www.php.net/manual/en/function.array.php