array_is_list

    (PHP 8 >= 8.1.0)

    array_is_list — Checks whether a given array is a list

    Description

    array_is_list(array $array): bool

    Determines if the given array is a list. An array is considered a list if its keys consist of consecutive numbers from 0 to count($array)-1.

    Parameters

    array

    The array being evaluated.

    Return Values

    Returns true if array is a list, false otherwise.

    Examples

    Example #1 array_is_list() example

    <?php

    array_is_list    ([]); // true
    array_is_list(['apple', 2, 3]); // true
    array_is_list([0 => 'apple', 'orange']); // true

    // The array does not start at 0
    array_is_list([1 => 'apple', 'orange']); // false

    // The keys are not in the correct order
    array_is_list([1 => 'apple', 0 => 'orange']); // false

    // Non-integer keys
    array_is_list([0 => 'apple', 'foo' => 'bar']); // false

    // Non-consecutive keys
    array_is_list([0 => 'apple', 2 => 'bar']); // false
    ?>

    Notes

    Note:

    This function returns true on empty arrays.

    See Also

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    User Contributed Notes 6 notes

    up
    50
    phpnet at jesseschalken dot com
    2 years ago
    Polyfills that call `array_keys()`, `array_values()` or `range()` are inefficient because they create new arrays unnecessarily.

    Please use this polyfill instead which creates no new arrays and only does a single pass over the given array.

    <?php

    if (!function_exists("array_is_list")) {
    function     array_is_list(array $array): bool
    {
    $i = 0;
    foreach (    $array as $k => $v) {
    if (    $k !== $i++) {
    return     false;
    }
    }
    return     true;
    }
    }

    ?>
    up
    23
    divinity76+spam at gmail dot com
    2 years ago
    slightly optimized version of phpnet at jesseschalken dot com's excellent array_is_list:

    <?php

    if (!function_exists("array_is_list")) {
    function     array_is_list(array $array): bool
    {
    $i = -1;
    foreach (    $array as $k => $v) {
    ++    $i;
    if (    $k !== $i) {
    return     false;
    }
    }
    return     true;
    }
    }

    ?>

    benchmarks: https://3v4l.org/9BPqL

    why is this faster you ask? because post-increment does more,

    here is what pre-increment actually means:
    step 1: increment the value by 1.
    step 2: return the value.

    here is what post-increment actually means:
    step 1: create a copy of the original value.
    step 2: increment the original value by 1.
    step 3: return the copy.

    another question might be "why didn't you write `if ($k !== ++$i) {` ? ... that is a good question! turns out that ++$i;if($k!==$i){...} is faster on PHP7 than if($k !== ++$i){...} for reasons unknown to me.. (if you have an answer, feel free to email me about it!)

    (i have NOT checked if PHP8/jit auto-optimize this stuff, but at least back in PHP7 it's true that pre-increment is faster than post-increment, and this polyfill is primarily for PHP7)
    up
    14
    Matteo Galletti
    3 years ago
    Polyfill implementation for PHP versions lower than 8.1.

    <?php
    if (!function_exists('array_is_list'))
    {
    function     array_is_list(array $a)
    {
    return     $a === [] || (array_keys($a) === range(0, count($a) - 1));
    }
    }
    ?>
    up
    -1
    2317216477 at qq dot com
    20 days ago
    function isIndexed($array)
    {
    if (is_array($array)) {
    $keys = array_keys($array);
    return $keys === array_keys($keys);
    }
    return false;
    }

    function isAssoc($array)
    {
    if (is_array($array)) {
    $keys = array_keys($array);
    return $keys !== array_keys($keys);
    }
    return false;
    }

    these two function is more faster than divinity76+spam at gmail dot com's about three times in my computer for PHP 8.2.9:

    array(3) {
    ["pre"]=>
    float(0.8179779052734375)
    ["post"]=>
    float(0.8116860389709473)
    ["index"]=>
    float(0.3369460105895996)
    }

    :)
    up
    1
    info at ensostudio dot ru
    3 years ago
    old school polyfill (:
    <?php
    if (!function_exists('array_is_list')) {
    function     array_is_list(array $array)
    {
    if (    $array === []) {
    return     true;
    }
    $keys = array_keys($array);
    return     $keys === array_keys($keys);
    }
    }
    ?>
    up
    0
    maruerru
    1 year ago
    I think, this is the fastest polyfill:

    <?php

    if (!function_exists('array_is_list')) {
    function     array_is_list(array $array)
    {
    return     $array === array_values($array);
    }
    }

    ?>
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