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PHP / array_is_list — DevDocs

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

  • array_values() - Return all the values of an array
PHP / array_key_exists — DevDocs

array_key_exists

(PHP 4 >= 4.0.7, PHP 5, PHP 7, PHP 8)

array_key_exists Checks if the given key or index exists in the array

Description

array_key_exists(string|int $key, array $array): bool

array_key_exists() returns true if the given key is set in the array. key can be any value possible for an array index.

Parameters

key

Value to check.

array

An array with keys to check.

Return Values

Returns true on success or false on failure.

Note :

array_key_exists() will search for the keys in the first dimension only. Nested keys in multidimensional arrays will not be found.

Examples

Example #1 array_key_exists() example

<?php
$search_array = array('first' => 1, 'second' => 4);
if (array_key_exists('first', $search_array)) {
    echo "The 'first' element is in the array";
}
?>

Example #2 array_key_exists() vs isset()

isset() does not return true for array keys that correspond to a null value, while array_key_exists() does.

<?php
$search_array = array('first' => null, 'second' => 4);

// returns false
isset($search_array['first']);

// returns true
array_key_exists('first', $search_array);
?>

Notes

Note :

For backward compatibility reasons, array_key_exists() will also return true if key is a property defined within an object given as array . This behaviour is deprecated as of PHP 7.4.0, and removed as of PHP 8.0.0.

To check whether a property exists in an object, property_exists() should be used.

See Also

  • isset() - Determine if a variable is declared and is different than null
  • array_keys() - Return all the keys or a subset of the keys of an array
  • in_array() - Checks if a value exists in an array
  • property_exists() - Checks if the object or class has a property
Read article
PHP / array_key_first — DevDocs

array_key_first

(PHP 7 >= 7.3.0, PHP 8)

array_key_first Gets the first key of an array

Description

array_key_first(array $array): int|string|null

Get the first key of the given array without affecting the internal array pointer.

Parameters

array

An array.

Return Values

Returns the first key of array if the array is not empty; null otherwise.

Examples

Example #1 Basic array_key_first() Usage

<?php
$array = ['a' => 1, 'b' => 2, 'c' => 3];

$firstKey = array_key_first($array);

var_dump($firstKey);
?>

The above example will output:

string(1) "a"

Notes

Tip

There are several ways to provide this functionality for versions prior to PHP 7.3.0. It is possible to use array_keys() , but that may be rather inefficient. It is also possible to use reset() and key() , but that may change the internal array pointer. An efficient solution, which does not change the internal array pointer, written as polyfill:

<?php
if (!function_exists('array_key_first')) {
    function array_key_first(array $arr) {
        foreach($arr as $key => $unused) {
            return $key;
        }
        return NULL;
    }
}
?>

See Also

  • array_key_last() - Gets the last key of an array
  • reset() - Set the internal pointer of an array to its first element
Read article
PHP / array_key_last — DevDocs

array_key_last

(PHP 7 >= 7.3.0, PHP 8)

array_key_last Gets the last key of an array

Description

array_key_last(array $array): int|string|null

Get the last key of the given array without affecting the internal array pointer.

Parameters

array

An array.

Return Values

Returns the last key of array if the array is not empty; null otherwise.

See Also

  • array_key_first() - Gets the first key of an array
  • end() - Set the internal pointer of an array to its last element
Read article
PHP / array_keys — DevDocs

array_keys

(PHP 4, PHP 5, PHP 7, PHP 8)

array_keys Return all the keys or a subset of the keys of an array

Description

array_keys(array $array): array
array_keys(array $array, mixed $filter_value, bool $strict = false): array

array_keys() returns the keys, numeric and string, from the array .

If a filter_value is specified, then only the keys for that value are returned. Otherwise, all the keys from the array are returned.

Parameters

array

An array containing keys to return.

filter_value

If specified, then only keys containing this value are returned.

strict

Determines if strict comparison (===) should be used during the search.

Return Values

Returns an array of all the keys in array .

Examples

Example #1 array_keys() example

<?php
$array = array(0 => 100, "color" => "red");
print_r(array_keys($array));

$array = array("blue", "red", "green", "blue", "blue");
print_r(array_keys($array, "blue"));

$array = array("color" => array("blue", "red", "green"),
               "size"  => array("small", "medium", "large"));
print_r(array_keys($array));
?>

The above example will output:

Array
(
    [0] => 0
    [1] => color
)
Array
(
    [0] => 0
    [1] => 3
    [2] => 4
)
Array
(
    [0] => color
    [1] => size
)

See Also

  • array_values() - Return all the values of an array
  • array_combine() - Creates an array by using one array for keys and another for its values
  • array_key_exists() - Checks if the given key or index exists in the array
  • array_search() - Searches the array for a given value and returns the first corresponding key if successful
Read article
PHP / array_map — DevDocs

array_map

(PHP 4 >= 4.0.6, PHP 5, PHP 7, PHP 8)

array_map Applies the callback to the elements of the given arrays

Description

array_map(?callable $callback, array $array, array ...$arrays): array

array_map() returns an array containing the results of applying the callback to the corresponding value of array (and arrays if more arrays are provided) used as arguments for the callback. The number of parameters that the callback function accepts should match the number of arrays passed to array_map() . Excess input arrays are ignored. An ArgumentCountError is thrown if an insufficient number of arguments is provided.

Parameters

callback

A callable to run for each element in each array.

null can be passed as a value to callback to perform a zip operation on multiple arrays. If only array is provided, array_map() will return the input array.

array

An array to run through the callback function.

arrays

Supplementary variable list of array arguments to run through the callback function.

Return Values

Returns an array containing the results of applying the callback function to the corresponding value of array (and arrays if more arrays are provided) used as arguments for the callback.

The returned array will preserve the keys of the array argument if and only if exactly one array is passed. If more than one array is passed, the returned array will have sequential integer keys.

Changelog

Version Description
8.0.0 If callback expects a parameter to be passed by reference, this function will now emit an E_WARNING .

Examples

Example #1 array_map() example

<?php
function cube($n)
{
    return ($n * $n * $n);
}

$a = [1, 2, 3, 4, 5];
$b = array_map('cube', $a);
print_r($b);
?>

This makes $b have:

Array
(
    [0] => 1
    [1] => 8
    [2] => 27
    [3] => 64
    [4] => 125
)

Example #2 array_map() using a lambda function

<?php
$func = function(int $value): int {
    return $value * 2;
};

print_r(array_map($func, range(1, 5)));

// Or as of PHP 7.4.0:

print_r(array_map(fn($value): int => $value * 2, range(1, 5)));

?>
Array
(
    [0] => 2
    [1] => 4
    [2] => 6
    [3] => 8
    [4] => 10
)

Example #3 array_map() - using more arrays

<?php
function show_Spanish(int $n, string $m): string
{
    return "The number {$n} is called {$m} in Spanish";
}

function map_Spanish(int $n, string $m): array
{
    return [$n => $m];
}

$a = [1, 2, 3, 4, 5];
$b = ['uno', 'dos', 'tres', 'cuatro', 'cinco'];

$c = array_map('show_Spanish', $a, $b);
print_r($c);

$d = array_map('map_Spanish', $a , $b);
print_r($d);
?>

The above example will output:

// printout of $c
Array
(
    [0] => The number 1 is called uno in Spanish
    [1] => The number 2 is called dos in Spanish
    [2] => The number 3 is called tres in Spanish
    [3] => The number 4 is called cuatro in Spanish
    [4] => The number 5 is called cinco in Spanish
)

// printout of $d
Array
(
    [0] => Array
        (
            [1] => uno
        )

    [1] => Array
        (
            [2] => dos
        )

    [2] => Array
        (
            [3] => tres
        )

    [3] => Array
        (
            [4] => cuatro
        )

    [4] => Array
        (
            [5] => cinco
        )

)

Usually when using two or more arrays, they should be of equal length because the callback function is applied in parallel to the corresponding elements. If the arrays are of unequal length, shorter ones will be extended with empty elements to match the length of the longest.

An interesting use of this function is to construct an array of arrays, which can be easily performed by using null as the name of the callback function

Example #4 Performing a zip operation of arrays

<?php
$a = [1, 2, 3, 4, 5];
$b = ['one', 'two', 'three', 'four', 'five'];
$c = ['uno', 'dos', 'tres', 'cuatro', 'cinco'];

$d = array_map(null, $a, $b, $c);
print_r($d);
?>

The above example will output:

Array
(
    [0] => Array
        (
            [0] => 1
            [1] => one
            [2] => uno
        )

    [1] => Array
        (
            [0] => 2
            [1] => two
            [2] => dos
        )

    [2] => Array
        (
            [0] => 3
            [1] => three
            [2] => tres
        )

    [3] => Array
        (
            [0] => 4
            [1] => four
            [2] => cuatro
        )

    [4] => Array
        (
            [0] => 5
            [1] => five
            [2] => cinco
        )

)

Example #5 null callback with only array

<?php
$array = [1, 2, 3];
var_dump(array_map(null, $array));
?>

The above example will output:

array(3) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  int(3)
}

Example #6 array_map() - with string keys

<?php
$arr = ['stringkey' => 'value'];
function cb1($a) {
    return [$a];
}
function cb2($a, $b) {
    return [$a, $b];
}
var_dump(array_map('cb1', $arr));
var_dump(array_map('cb2', $arr, $arr));
var_dump(array_map(null,  $arr));
var_dump(array_map(null, $arr, $arr));
?>

The above example will output:

array(1) {
  ["stringkey"]=>
  array(1) {
    [0]=>
    string(5) "value"
  }
}
array(1) {
  [0]=>
  array(2) {
    [0]=>
    string(5) "value"
    [1]=>
    string(5) "value"
  }
}
array(1) {
  ["stringkey"]=>
  string(5) "value"
}
array(1) {
  [0]=>
  array(2) {
    [0]=>
    string(5) "value"
    [1]=>
    string(5) "value"
  }
}

Example #7 array_map() - associative arrays

While array_map() does not directly support using the array key as an input, that may be simulated using array_keys() .

<?php
$arr = [
    'v1' => 'First release',
    'v2' => 'Second release',
    'v3' => 'Third release',
];

// Note: Before 7.4.0, use the longer syntax for anonymous functions instead.
$callback = fn(string $k, string $v): string => "$k was the $v";

$result = array_map($callback, array_keys($arr), array_values($arr));

var_dump($result);
?>

The above example will output:

array(3) {
  [0]=>
  string(24) "v1 was the First release"
  [1]=>
  string(25) "v2 was the Second release"
  [2]=>
  string(24) "v3 was the Third release"
}

See Also

  • array_filter() - Filters elements of an array using a callback function
  • array_reduce() - Iteratively reduce the array to a single value using a callback function
  • array_walk() - Apply a user supplied function to every member of an array
Read article

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