Extract Unique Values from an Array

<?php
$colors = ['red', 'green', 'blue', 'red', 'yellow', 'green'];

// Get unique values, preserving the first encountered key
$uniqueColors = array_unique($colors);

echo "Original Colors:
";
print_r($colors);
echo "
Unique Colors (keys preserved):
";
print_r($uniqueColors);

$numbers = [1, 2, 3, 2, 1, 4, 5, 4];

// Get unique values and re-index the array
$uniqueNumbersReindexed = array_values(array_unique($numbers));

echo "
Original Numbers:
";
print_r($numbers);
echo "
Unique Numbers (re-indexed):
";
print_r($uniqueNumbersReindexed);

$users = [
    ['id' => 1, 'name' => 'Alice'],
    ['id' => 2, 'name' => 'Bob'],
    ['id' => 1, 'name' => 'Alice'], // Duplicate
    ['id' => 3, 'name' => 'Charlie'],
    ['id' => 2, 'name' => 'Bob']  // Duplicate
];

// Get unique associative arrays based on a specific key (e.g., 'id')
// A more complex example, often done by looping or using array_reduce
$uniqueUsersById = array_reduce($users, function ($carry, $item) {
    $found = false;
    foreach ($carry as $existingItem) {
        if ($existingItem['id'] === $item['id']) {
            $found = true;
            break;
        }
    }
    if (!$found) {
        $carry[] = $item;
    }
    return $carry;
}, []);

echo "
Unique Users by ID:
";
print_r($uniqueUsersById);
?>