PHP Array Functions II

Now let's explore array functions that modify arrays - adding, removing, merging, slicing, and restructuring elements. These functions are essential for dynamic data manipulation.

Adding Elements

<?php
$stack = ["A", "B"];

// Add to end
array_push($stack, "C", "D");  // ["A", "B", "C", "D"]

// Shorthand (single element)
$stack[] = "E";                // ["A", "B", "C", "D", "E"]

// Add to beginning
array_unshift($stack, "Z");    // ["Z", "A", "B", "C", "D", "E"]
?>

Click Run to execute your code

Removing Elements

<?php
$queue = ["First", "Second", "Third", "Fourth"];

// Remove from end
$last = array_pop($queue);
echo $last;  // "Fourth"
// $queue: ["First", "Second", "Third"]

// Remove from beginning
$first = array_shift($queue);
echo $first;  // "First"
// $queue: ["Second", "Third"]

// Remove specific element
unset($queue[0]);
// $queue: [1 => "Third"] - Note: doesn't reindex!

// Reindex after unset
$queue = array_values($queue);
// $queue: [0 => "Third"]
?>

Merging Arrays

array_merge()

<?php
// Indexed arrays - concatenates
$a = [1, 2, 3];
$b = [4, 5, 6];
$merged = array_merge($a, $b);  // [1, 2, 3, 4, 5, 6]

// Associative arrays - later values overwrite
$defaults = ["color" => "red", "size" => "M"];
$custom = ["size" => "L", "qty" => 2];
$config = array_merge($defaults, $custom);
// ["color" => "red", "size" => "L", "qty" => 2]
?>

Spread Operator (PHP 7.4+)

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

// Combine with spread
$all = [...$first, ...$second];  // [1, 2, 3, 4, 5, 6]

// Insert in middle
$middle = [...$first, "X", ...$second];
// [1, 2, 3, "X", 4, 5, 6]
?>

array_combine()

Create an associative array from two arrays:

<?php
$headers = ["Name", "Email", "Age"];
$values = ["John", "[email protected]", 30];

$row = array_combine($headers, $values);
// ["Name" => "John", "Email" => "[email protected]", "Age" => 30]

// Useful for CSV processing
$csvHeader = ["id", "product", "price"];
$csvRow = ["101", "Widget", "29.99"];
$record = array_combine($csvHeader, $csvRow);
?>

Slicing Arrays

array_slice()

Extract a portion without modifying original:

<?php
$arr = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];

// slice(offset, length)
array_slice($arr, 2, 4);    // [2, 3, 4, 5]
array_slice($arr, 5);       // [5, 6, 7, 8, 9]
array_slice($arr, -3);      // [7, 8, 9]
array_slice($arr, 0, -2);   // [0, 1, 2, 3, 4, 5, 6, 7]
array_slice($arr, 2, -2);   // [2, 3, 4, 5, 6, 7]

// Preserve keys
$assoc = ["a" => 1, "b" => 2, "c" => 3];
array_slice($assoc, 1, 2, true);  // ["b" => 2, "c" => 3]
?>

array_splice()

Remove/replace portion AND modify original:

<?php
// Remove elements
$arr = ["a", "b", "c", "d", "e"];
$removed = array_splice($arr, 2, 2);  // Remove 2 at index 2
// $removed: ["c", "d"]
// $arr: ["a", "b", "e"]

// Replace elements
$arr = ["a", "b", "c", "d", "e"];
array_splice($arr, 1, 2, ["X", "Y", "Z"]);
// $arr: ["a", "X", "Y", "Z", "d", "e"]

// Insert elements (length = 0)
$arr = ["a", "b", "e"];
array_splice($arr, 2, 0, ["c", "d"]);
// $arr: ["a", "b", "c", "d", "e"]
?>

Other Useful Functions

<?php
// array_flip - Swap keys and values
$arr = ["a" => 1, "b" => 2, "c" => 3];
array_flip($arr);  // [1 => "a", 2 => "b", 3 => "c"]

// array_reverse - Reverse order
$arr = [1, 2, 3, 4, 5];
array_reverse($arr);  // [5, 4, 3, 2, 1]

// array_chunk - Split into chunks
$arr = [1, 2, 3, 4, 5, 6, 7];
array_chunk($arr, 3);
// [[1, 2, 3], [4, 5, 6], [7]]

// array_pad - Pad to specified length
$arr = [1, 2, 3];
array_pad($arr, 5, 0);   // [1, 2, 3, 0, 0]
array_pad($arr, -5, 0);  // [0, 0, 1, 2, 3]

// array_fill_keys - Create with same value
$keys = ["a", "b", "c"];
array_fill_keys($keys, 0);  // ["a" => 0, "b" => 0, "c" => 0]
?>

Quick Reference

Exercise: Playlist Manager

<?php
class Playlist {
    private $songs = [];

    // Add to end
    public function add($song) {
        $this->songs[] = $song;
    }

    // Add to beginning (play next)
    public function playNext($song) {
        array_unshift($this->songs, $song);
    }

    // Remove current (first song)
    public function skipCurrent() {
        return array_shift($this->songs);
    }

    // Move song to new position
    public function moveSong($fromIndex, $toIndex) {
        $song = array_splice($this->songs, $fromIndex, 1);
        array_splice($this->songs, $toIndex, 0, $song);
    }

    // Merge another playlist
    public function merge($otherSongs) {
        $this->songs = array_merge($this->songs, $otherSongs);
    }

    public function show() {
        foreach ($this->songs as $i => $song) {
            echo ($i + 1) . ". $song\n";
        }
    }
}

$playlist = new Playlist();
$playlist->add("Song A");
$playlist->add("Song B");
$playlist->add("Song C");

echo "Initial playlist:\n";
$playlist->show();

$playlist->playNext("Urgent Song");
echo "\nAfter playNext:\n";
$playlist->show();

$skipped = $playlist->skipCurrent();
echo "\nSkipped: $skipped\n";
$playlist->show();

$playlist->merge(["Song X", "Song Y"]);
echo "\nAfter merge:\n";
$playlist->show();
?>

Summary

What's Next?

Now let's explore Array Iteration - powerful functions like array_map(), array_filter(), and array_reduce() for functional-style array processing!