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

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

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

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

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

Notes

Note:
This function returns true on empty arrays.

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User Contributed Notes 6 notes

down

phpnet at jesseschalken dot com ¶

3 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;
    }
}

?>

down

divinity76+spam at gmail dot com ¶

3 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)

down

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));
    }
}
?>

down

-1

2317216477 at qq dot com ¶

8 months 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)
}

:)

down

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);
    }
}
?>

down

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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array_is_list

Description

Parameters

Return Values

Examples

Notes

See Also

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User Contributed Notes 6 notes