Arrays & Collections 📦

<?php
// An INDEXED array is an ordered list. Keys are numbers, starting at 0.
$fruits = ["Apple", "Banana", "Cherry"];   // [] is the short array syntax

echo $fruits[0] . "\n";          // Apple   — first item is index 0
echo $fruits[2] . "\n";          // Cherry  — third item is index 2
echo count($fruits) . "\n";      // 3       — how many items are in the array

// Add to the END with $array[] = ... (PHP picks the next number for you)
$fruits[] = "Date";               // now index 3 holds "Date"
echo count($fruits) . "\n";      // 4

// implode() joins every item into one string with a separator between them
echo implode(", ", $fruits) . "\n";   // Apple, Banana, Cherry, Date
?>

Apple
Cherry
3
4
Apple, Banana, Cherry, Date

<?php
// An ASSOCIATIVE array maps your OWN keys (usually strings) to values.
// Syntax: ['key' => 'value']  — the => arrow reads as "points to".
$person = [
    "name" => "Alice",
    "age"  => 28,
    "city" => "London",
];

echo $person["name"] . "\n";     // Alice  — look a value up BY its key
echo $person["age"] . "\n";      // 28

// Add or update by assigning to a key
$person["role"] = "Developer";    // new key
$person["age"]  = 29;             // overwrites the old value

// Inside "double quotes" wrap an array lookup in { } to print it cleanly
echo "{$person['name']} is {$person['age']}, role {$person['role']}\n";
// Alice is 29, role Developer
?>

Alice
28
Alice is 29, role Developer

<?php
// A MULTIDIMENSIONAL array is an array whose values are themselves arrays.
// Here each row is an associative array describing one student.
$students = [
    ["name" => "Alice", "grade" => 95],
    ["name" => "Bob",   "grade" => 87],
    ["name" => "Cara",  "grade" => 92],
];

// foreach walks the list one row at a time; $s is the current inner array
foreach ($students as $s) {
    // Reach into a nested value with TWO sets of brackets
    echo "{$s['name']}: {$s['grade']}\n";
}

// Reach a single nested value directly: outer index, then inner key
echo "First student: {$students[0]['name']}\n";   // Alice
?>

Alice: 95
Bob: 87
Cara: 92
First student: Alice

<?php
$queue = ["Alice", "Bob"];

// --- ADDING ---
$queue[] = "Cara";                // append one item (shortest way)
array_push($queue, "Dan", "Eve"); // push one OR MORE onto the end
array_unshift($queue, "Zoe");     // add to the FRONT (everything shifts right)
echo implode(", ", $queue) . "\n";
// Zoe, Alice, Bob, Cara, Dan, Eve

// --- REMOVING ---
$last  = array_pop($queue);       // remove & RETURN the last item -> "Eve"
$first = array_shift($queue);     // remove & RETURN the first item -> "Zoe"
echo "Popped $last, shifted $first\n";

// unset() deletes a specific key (note: it does NOT renumber the rest)
unset($queue[1]);                 // removes "Bob"; indexes now 0, 2, 3...
echo implode(", ", $queue) . "\n";   // Alice, Cara, Dan
?>

Zoe, Alice, Bob, Cara, Dan, Eve
Popped Eve, shifted Zoe
Alice, Cara, Dan

<?php
$nums = [5, 2, 8, 1, 9, 3];

// array_map: TRANSFORM every item. Order: (callback, array). Returns a NEW array.
$doubled = array_map(fn($n) => $n * 2, $nums);
echo implode(", ", $doubled) . "\n";     // 10, 4, 16, 2, 18, 6

// array_filter: KEEP items where the callback is true. Order: (array, callback).
$evens = array_filter($nums, fn($n) => $n % 2 === 0);
echo implode(", ", $evens) . "\n";       // 8 (only the even numbers survive)

// array_reduce: BOIL the array down to ONE value. Order: (array, callback, start).
$total = array_reduce($nums, fn($carry, $n) => $carry + $n, 0);
echo "Sum: $total\n";                     // Sum: 28

// Membership & keys/values
echo in_array(8, $nums) ? "has 8\n" : "no 8\n";   // has 8
$prices = ["pen" => 2, "pad" => 5];
echo implode(", ", array_keys($prices)) . "\n";    // pen, pad
echo implode(", ", array_values($prices)) . "\n";  // 2, 5

// implode joins to a string; explode splits a string back into an array
$csv = implode("-", [2024, 6, 16]);        // "2024-6-16"
$parts = explode("-", $csv);               // ["2024", "6", "16"]
echo "$csv -> {$parts[1]}\n";             // 2024-6-16 -> 6
?>

10, 4, 16, 2, 18, 6
8
Sum: 28
has 8
pen, pad
2, 5
2024-6-16 -> 6

<?php
// 🎯 YOUR TURN — fill in each blank marked ___ , then run it.

// 1) Make an indexed array of three colours
$colours = ___;            // 👉 e.g.  ["red", "green", "blue"]

// 2) Append "yellow" to the END using the [] shortcut
$colours___ = "yellow";    // 👉 put [] right after $colours

// 3) Print how many colours there are now
echo ___($colours) . "\n"; // 👉 the function that counts items

// 4) Join them into one line separated by ", "
echo ___(", ", $colours) . "\n";   // 👉 the function that joins to a string

// ✅ Expected output:
//    4
//    red, green, blue, yellow
?>

4
red, green, blue, yellow

<?php
// sort() reorders an INDEXED array in place (ascending) and renumbers keys.
$nums = [5, 2, 8, 1];
sort($nums);
echo implode(", ", $nums) . "\n";         // 1, 2, 5, 8

// For ASSOCIATIVE arrays use asort()/ksort() so keys stay attached.
$scores = ["Bob" => 87, "Alice" => 95, "Cara" => 92];
asort($scores);                            // sort by VALUE, keep keys
echo implode(", ", array_keys($scores)) . "\n";   // Bob, Cara, Alice
ksort($scores);                            // sort by KEY (alphabetical)
echo implode(", ", array_keys($scores)) . "\n";   // Alice, Bob, Cara

// usort() sorts with YOUR rule. Return negative/zero/positive to order pairs.
$people = [["n" => "Al", "age" => 30], ["n" => "Bo", "age" => 22]];
usort($people, fn($a, $b) => $a["age"] - $b["age"]);  // youngest first
echo "{$people[0]['n']} is youngest\n";   // Bo is youngest

// Spread ... and list() destructuring
$more = [4, 5];
$all  = [1, 2, 3, ...$more];                // spread merges arrays: 1,2,3,4,5
echo implode(", ", $all) . "\n";          // 1, 2, 3, 4, 5
[$x, $y] = [10, 20];                        // list() unpacks into variables
echo "$x and $y\n";                        // 10 and 20
?>

1, 2, 5, 8
Bob, Cara, Alice
Alice, Bob, Cara
Bo is youngest
1, 2, 3, 4, 5
10 and 20

<?php
// 🎯 YOUR TURN — build a contact card with an associative array.

// 1) Create an associative array with keys "name" and "email"
$contact = [
    "name"  => ___,        // 👉 a name in "double quotes"
    "email" => ___,        // 👉 an email in "double quotes"
];

// 2) Add a "city" key AFTER creating the array
$contact[___] = "Paris";   // 👉 the key name, in quotes

// 3) Loop over every key => value pair and print it
foreach ($contact as $key => $value) {
    echo "$key: $value\n";
}

// ✅ Expected output (example):
//    name: Sam
//    email: sam@mail.com
//    city: Paris
?>

name: Sam
email: sam@mail.com
city: Paris