Arrays

By the end of this lesson you'll store many values in one variable — ordered lists, key-value records, and nested tables — and reshape them at will with PHP's array functions, the everyday workhorse of real applications.

Part of the free Php course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

What You'll Learn in This Lesson

1️⃣ Indexed Arrays — Ordered Lists

An array is a single variable that holds many values. The simplest kind is an indexed array — an ordered list where PHP labels each slot with a number starting at 0 , not 1. You create one with the modern short syntax [ ] (older code uses array(...) — same thing). You read a slot by its index, and you tack a value onto the end with the handy $array[] = ... shortcut, which lets PHP pick the next number for you.

2️⃣ Associative Arrays — Key → Value

When position isn't meaningful but a label is, use an associative array . Instead of numbers, you choose your own keys — usually strings — and pair each with a value using the => arrow (read it as "points to"). This is how PHP models a record: a user, a config setting, a row from a database. You look values up by key, and assigning to a new key adds it while assigning to an existing key overwrites it.

Notice the { $person['name'] } trick: inside a double-quoted string, wrapping an array lookup in curly braces lets PHP drop the value in cleanly. Without the braces, "$person['name']" confuses the parser.

3️⃣ Multidimensional Arrays & foreach

Because an array's values can themselves be arrays, you can build tables and nested structures — a list of records, a grid, JSON-shaped data. To walk through any array, reach for foreach : it hands you each element in turn without you tracking an index. To reach a nested value, stack the brackets: outer position, then inner key.

4️⃣ Adding & Removing Items

Arrays are not fixed in size — you grow and shrink them as the program runs. Append with the $a[] = shortcut or array_push (which can add several at once); add to the front with array_unshift . Remove and capture the last item with array_pop or the first with array_shift . To delete one specific element by key, use unset — but note it leaves a gap in the numbering rather than renumbering.

5️⃣ Transforming Data — map, filter, reduce

The real power of PHP arrays is its library of built-in functions. Three are worth learning by heart. array_map applies a function to every element and returns a new array. array_filter keeps only the elements your test returns true for. array_reduce boils the whole array down to a single value (a sum, a max, a joined string). Watch the argument order — array_map(fn, array) but array_filter(array, fn) . Alongside them, in_array , array_keys , array_values , and the string pair implode / explode cover most everyday needs.

Now you try. The script below is almost complete — fill in each ___ using the 👉 hint, then run it and check it against the Output panel.

6️⃣ Sorting, Merging & Unpacking

sort reorders an indexed list ascending — but it renumbers the keys , so on an associative array it would throw your labels away. For keyed data use asort (by value) or ksort (by key); for a custom rule use usort with a comparison function. To combine arrays, use array_merge or the newer spread operator ... ; and list() destructuring — written as [$x, $y] = [...] — unpacks an array straight into separate variables.

One more. Build a small contact card as an associative array, then loop it with foreach ($arr as $key => $value) , which hands you both halves of each pair.

Common Errors (and the fix)

• "Warning: Undefined array key 'email'" — you read a key that doesn't exist (a typo, or it was never set). PHP returns null and warns. Guard it with isset($a['email']) or supply a default with the null-coalescing operator: $a['email'] ?? 'none' .
• array_map and array_filter take their arguments in opposite orders — it's array_map(fn, $arr) but array_filter($arr, fn) . Swap them by mistake and you'll get a "TypeError: argument must be callable". When in doubt, the array comes second in map and first in filter/reduce.
• Your keys vanished after sorting an associative array — sort() (and rsort() ) reindex from 0, discarding string keys. To keep key→value pairs intact, use asort() / arsort() to sort by value, or ksort() to sort by key.
• "PHP Parse error: syntax error, unexpected '=>'" — you used the => arrow outside an array, or mixed it up with assignment = . The arrow only links a key to a value inside array brackets or a foreach .

Pro Tips

• 💡 Reach for map/filter/reduce before writing a loop. They state your intent ("transform", "keep", "total") and avoid off-by-one bugs from manual indexing.
• 💡 Use $a['key'] ?? $default whenever a key might be missing — it's the clean, warning-free way to read optional data.
• 💡 Pick one style per array. A purely indexed list or a purely associative record reads far clearer than one that mixes numeric and string keys.

📋 Quick Reference — PHP Arrays

Syntax / Function

Example

What It Does

[ ]

$a = [1, 2, 3];

Create an array (short syntax)

=>

["name" => "Al"]

Map a key to a value

$a[] =

$a[] = 4;

Append to the end

unset()

unset($a[1]);

Delete one key (no renumber)

count()

count($a)

Number of items

in_array()

in_array(2, $a)

Is a value present? (bool)

array_map()

array_map($fn, $a)

Transform every element

array_filter()

array_filter($a, $fn)

Keep matching elements

array_reduce()

array_reduce($a, $fn, 0)

Boil down to one value

sort() / usort()

usort($a, $cmp)

Reorder (renumbers keys)

asort() / ksort()

ksort($a)

Sort, keeping keys

array_merge()

array_merge($a, $b)

Combine arrays

implode() / explode()

implode(",", $a)

Array ↔ string

... / [ ] =

[...$a]; [$x] = $a;

Spread / list() unpack

Frequently Asked Questions

Mini-Challenge: Top Scorers

No code is filled in this time — just a brief and an outline. Write it yourself, run it on onecompiler.com/php or your own machine, then check your result against the expected output in the comments. This combines array_filter , usort , foreach and array_reduce — the real toolkit.

🎉 Lesson Complete!

• ✅ Indexed arrays are ordered lists keyed by numbers from 0 ; associative arrays map your own keys with =>
• ✅ Arrays nest: a multidimensional array holds arrays, and foreach walks any of them
• ✅ Grow and shrink with $a[] = , array_push/pop/shift/unshift , and unset
• ✅ array_map , array_filter , and array_reduce transform, keep, and combine data (mind the argument order)
• ✅ sort renumbers keys; use asort / ksort / usort to keep or customise order
• ✅ implode / explode , spread ... , and list() move data between arrays, strings, and variables
• ✅ Next lesson: File Handling — read and write files on the server

Practice quiz

Continue this course

• Previous: Functions
• Next: File Handling