array_unique() / array_reverse() / array_pad()

array_unique(array, sort_flags);

// Reverses the order of elements in an array
array_reverse(array, preserve_keys);

// Pads an array to the specified length with a value
array_pad(array, size, value);

array_fill(start_index, count, value);

sample_array_unique.php

<?php
// Remove duplicate Eva pilots
$pilots = ['Ikari Shinji', 'Ayanami Rei', 'Soryu Asuka Langley', 'Ikari Shinji', 'Nagisa Kaworu', 'Ayanami Rei'];
$unique = array_unique($pilots);
print_r($unique); // duplicates removed, leaving 4 elements

// Keys may be non-consecutive — re-index with array_values
$clean = array_values($unique);
print_r($clean); // keys are now sequential starting from 0

// Reverse the order of an array
$ranking = ['Ikari Shinji', 'Ayanami Rei', 'Soryu Asuka Langley'];
$reversed = array_reverse($ranking);
print_r($reversed);

// Pad an array to a specified length
$scores = [80, 90, 70];
$padded_right = array_pad($scores, 5, 0);
print_r($padded_right); // 0s added at the end, 5 elements total

$padded_left = array_pad($scores, -5, 0);
print_r($padded_left); // 0s added at the beginning, 5 elements total

$zeros = array_fill(0, 5, 0);
print_r($zeros);

array_unique.php

php array_unique.php
Array
(
    [0] => Ikari Shinji
    [1] => Ayanami Rei
    [2] => Soryu Asuka Langley
    [4] => Nagisa Kaworu
)
Array
(
    [0] => Ikari Shinji
    [1] => Ayanami Rei
    [2] => Soryu Asuka Langley
    [3] => Nagisa Kaworu
)
Array
(
    [0] => Soryu Asuka Langley
    [1] => Ayanami Rei
    [2] => Ikari Shinji
)
Array
(
    [0] => 80
    [1] => 90
    [2] => 70
    [3] => 0
    [4] => 0
)
Array
(
    [0] => 0
    [1] => 0
    [2] => 80
    [3] => 90
    [4] => 70
)
Array
(
    [0] => 0
    [1] => 0
    [2] => 0
    [3] => 0
    [4] => 0
)

array_unique() removes duplicate values from an array, but the original keys are preserved, which can result in non-consecutive keys. If you need sequential keys, combine it with array_values(). By default, values are compared as strings; passing SORT_REGULAR as the second argument compares them without type conversion.

array_reverse() returns a new array with the elements in reverse order. Passing true as the second argument preserves the original keys. You can also use it to reverse the order of a sorted array.

array_pad() pads from the beginning if the size is negative, or from the end if it is positive. If the array is already at least as large as the specified size, nothing changes. array_fill() is a convenient way to create an array pre-filled with a uniform initial value.

For sorting arrays, see sort() / rsort().

array_unique() preserves the original keys, so after removing duplicates the keys may be non-consecutive. Use array_values() to re-index them if sequential keys are needed.

<?php
$pilots = ['Ikari Shinji', 'Ayanami Rei', 'Ikari Shinji', 'Katsuragi Misato'];
$unique = array_unique($pilots);
print_r($unique); // keys: 0, 1, 3 (2 is missing)

// Re-index with array_values() when sequential keys are required
$clean = array_values($unique);
print_r($clean); // keys: 0, 1, 2

unique_keys.php

php unique_keys.php
Array
(
    [0] => Ikari Shinji
    [1] => Ayanami Rei
    [3] => Katsuragi Misato
)
Array
(
    [0] => Ikari Shinji
    [1] => Ayanami Rei
    [2] => Katsuragi Misato
)

By default, values are compared as strings, so 1 and "1" are treated as equal and one is removed. Using SORT_REGULAR makes the comparison type-aware.

<?php
$data = [1, "1", true, 1.0];

// Default (SORT_STRING): compared as strings
$default = array_unique($data);
print_r($default); // only 1 element remains

// SORT_REGULAR: type-aware comparison
$regular = array_unique($data, SORT_REGULAR);
print_r($regular); // may retain more elements

unique_types.php

php unique_types.php
Array
(
    [0] => 1
)
Array
(
    [0] => 1
)

When working with arrays that mix types, verify the result matches your intent beforehand.

Using array_unique() on a multidimensional array triggers a notice and does not work as expected. A different approach is needed to remove duplicate rows.

Problematic pattern (triggers a notice):

<?php
$characters = [
    ['name' => 'Ikari Shinji', 'unit' => 'Unit-01'],
    ['name' => 'Ayanami Rei', 'unit' => 'Unit-00'],
    ['name' => 'Ikari Shinji', 'unit' => 'Unit-01'], // duplicate
];

// Using array_unique directly on a multidimensional array causes a notice
$result = array_unique($characters); // Notice: Array to string conversion
print_r($result);

unique_multi_ng.php

php unique_multi_ng.php
Notice: Array to string conversion

Using json_encode/decode (working approach):

<?php
$characters = [
    ['name' => 'Ikari Shinji', 'unit' => 'Unit-01'],
    ['name' => 'Ayanami Rei', 'unit' => 'Unit-00'],
    ['name' => 'Ikari Shinji', 'unit' => 'Unit-01'], // duplicate
];

$unique = array_values(array_unique(array_map('json_encode', $characters)));
$unique = array_map('json_decode', $unique);
print_r($unique);

unique_multi_ok.php

php unique_multi_ok.php
Array
(
    [0] => stdClass Object
        (
            [name] => Ikari Shinji
            [unit] => Unit-01
        )
    [1] => stdClass Object
        (
            [name] => Ayanami Rei
            [unit] => Unit-00
        )
)

Deduplicating tags

Removing duplicate character attribute tags and formatting them as a list.

<?php
$tags_raw = ['Pilot', 'NERV', 'Pilot', 'Angel', 'NERV', 'Nagisa Kaworu'];
$tags = array_values(array_unique($tags_raw));
echo implode(', ', $tags);

unique_tags.php

php unique_tags.php
Pilot, NERV, Angel, Nagisa Kaworu

Setting defaults with array_pad

Initializing deployment flags for 5 pilots and setting some to active.

<?php
$active = [1, 1]; // Ikari Shinji and Ayanami Rei are deployed
$flags = array_pad($active, 5, 0); // fill 5 slots with default 0
print_r($flags);

unique_pad.php

php unique_pad.php
Array
(
    [0] => 1
    [1] => 1
    [2] => 0
    [3] => 0
    [4] => 0
)