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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
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
PHP / array_merge — DevDocs

array_merge

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

array_merge Merge one or more arrays

Description

array_merge(array ...$arrays): array

Merges the elements of one or more arrays together so that the values of one are appended to the end of the previous one. It returns the resulting array.

If the input arrays have the same string keys, then the later value for that key will overwrite the previous one. If, however, the arrays contain numeric keys, the later value will not overwrite the original value, but will be appended.

Values in the input arrays with numeric keys will be renumbered with incrementing keys starting from zero in the result array.

Parameters

arrays

Variable list of arrays to merge.

Return Values

Returns the resulting array. If called without any arguments, returns an empty array .

Changelog

Version Description
7.4.0 This function can now be called without any parameter. Formerly, at least one parameter has been required.

Examples

Example #1 array_merge() example

<?php
$array1 = array("color" => "red", 2, 4);
$array2 = array("a", "b", "color" => "green", "shape" => "trapezoid", 4);
$result = array_merge($array1, $array2);
print_r($result);
?>

The above example will output:

Array
(
    [color] => green
    [0] => 2
    [1] => 4
    [2] => a
    [3] => b
    [shape] => trapezoid
    [4] => 4
)

Example #2 Simple array_merge() example

<?php
$array1 = array();
$array2 = array(1 => "data");
$result = array_merge($array1, $array2);
?>

Don't forget that numeric keys will be renumbered!

Array
(
    [0] => data
)

If you want to append array elements from the second array to the first array while not overwriting the elements from the first array and not re-indexing, use the + array union operator:

<?php
$array1 = array(0 => 'zero_a', 2 => 'two_a', 3 => 'three_a');
$array2 = array(1 => 'one_b', 3 => 'three_b', 4 => 'four_b');
$result = $array1 + $array2;
var_dump($result);
?>

The keys from the first array will be preserved. If an array key exists in both arrays, then the element from the first array will be used and the matching key's element from the second array will be ignored.

array(5) {
  [0]=>
  string(6) "zero_a"
  [2]=>
  string(5) "two_a"
  [3]=>
  string(7) "three_a"
  [1]=>
  string(5) "one_b"
  [4]=>
  string(6) "four_b"
}

Example #3 array_merge() with non-array types

<?php
$beginning = 'foo';
$end = array(1 => 'bar');
$result = array_merge((array)$beginning, (array)$end);
print_r($result);
?>

The above example will output:

    Array
    (
        [0] => foo
        [1] => bar
    )

See Also

  • array_merge_recursive() - Merge one or more arrays recursively
  • array_replace() - Replaces elements from passed arrays into the first array
  • array_combine() - Creates an array by using one array for keys and another for its values
  • array operators
Read article
PHP / array_merge_recursive — DevDocs

array_merge_recursive

(PHP 4 >= 4.0.1, PHP 5, PHP 7, PHP 8)

array_merge_recursive Merge one or more arrays recursively

Description

array_merge_recursive(array ...$arrays): array

array_merge_recursive() merges the elements of one or more arrays together so that the values of one are appended to the end of the previous one. It returns the resulting array.

If the input arrays have the same string keys, then the values for these keys are merged together into an array, and this is done recursively, so that if one of the values is an array itself, the function will merge it with a corresponding entry in another array too. If, however, the arrays have the same numeric key, the later value will not overwrite the original value, but will be appended.

Parameters

arrays

Variable list of arrays to recursively merge.

Return Values

An array of values resulted from merging the arguments together. If called without any arguments, returns an empty array .

Changelog

Version Description
7.4.0 This function can now be called without any parameter. Formerly, at least one parameter has been required.

Examples

Example #1 array_merge_recursive() example

<?php
$ar1 = array("color" => array("favorite" => "red"), 5);
$ar2 = array(10, "color" => array("favorite" => "green", "blue"));
$result = array_merge_recursive($ar1, $ar2);
print_r($result);
?>

The above example will output:

Array
(
    [color] => Array
        (
            [favorite] => Array
                (
                    [0] => red
                    [1] => green
                )

            [0] => blue
        )

    [0] => 5
    [1] => 10
)

See Also

  • array_merge() - Merge one or more arrays
  • array_replace_recursive() - Replaces elements from passed arrays into the first array recursively
Read article
PHP / array_multisort — DevDocs

array_multisort

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

array_multisort Sort multiple or multi-dimensional arrays

Description

array_multisort(
 array &$array1,
 mixed $array1_sort_order = SORT_ASC,
 mixed $array1_sort_flags = SORT_REGULAR,
 mixed ...$rest
): bool

array_multisort() can be used to sort several arrays at once, or a multi-dimensional array by one or more dimensions.

Associative ( string ) keys will be maintained, but numeric keys will be re-indexed.

Note :

If two members compare as equal, they retain their original order. Prior to PHP 8.0.0, their relative order in the sorted array was undefined.

Note :

Resets array's internal pointer to the first element.

Parameters

array1

An array being sorted.

array1_sort_order

The order used to sort the previous array argument. Either SORT_ASC to sort ascendingly or SORT_DESC to sort descendingly.

This argument can be swapped with array1_sort_flags or omitted entirely, in which case SORT_ASC is assumed.

array1_sort_flags

Sort options for the previous array argument:

Sorting type flags:

  • SORT_REGULAR - compare items normally (don't change types)
  • SORT_NUMERIC - compare items numerically
  • SORT_STRING - compare items as strings
  • SORT_LOCALE_STRING - compare items as strings, based on the current locale. It uses the locale, which can be changed using setlocale()
  • SORT_NATURAL - compare items as strings using "natural ordering" like natsort()
  • SORT_FLAG_CASE - can be combined (bitwise OR) with SORT_STRING or SORT_NATURAL to sort strings case-insensitively

This argument can be swapped with array1_sort_order or omitted entirely, in which case SORT_REGULAR is assumed.

rest

More arrays, optionally followed by sort order and flags. Only elements corresponding to equivalent elements in previous arrays are compared. In other words, the sort is lexicographical.

Return Values

Returns true on success or false on failure.

Examples

Example #1 Sorting multiple arrays

<?php
$ar1 = array(10, 100, 100, 0);
$ar2 = array(1, 3, 2, 4);
array_multisort($ar1, $ar2);

var_dump($ar1);
var_dump($ar2);
?>

In this example, after sorting, the first array will contain 0, 10, 100, 100. The second array will contain 4, 1, 2, 3. The entries in the second array corresponding to the identical entries in the first array (100 and 100) were sorted as well.

array(4) {
  [0]=> int(0)
  [1]=> int(10)
  [2]=> int(100)
  [3]=> int(100)
}
array(4) {
  [0]=> int(4)
  [1]=> int(1)
  [2]=> int(2)
  [3]=> int(3)
}

Example #2 Sorting multi-dimensional array

<?php
$ar = array(
       array("10", 11, 100, 100, "a"),
       array(   1,  2, "2",   3,   1)
      );
array_multisort($ar[0], SORT_ASC, SORT_STRING,
                $ar[1], SORT_NUMERIC, SORT_DESC);
var_dump($ar);
?>

In this example, after sorting, the first array will transform to "10", 100, 100, 11, "a" (it was sorted as strings in ascending order). The second will contain 1, 3, "2", 2, 1 (sorted as numbers, in descending order).

array(2) {
  [0]=> array(5) {
    [0]=> string(2) "10"
    [1]=> int(100)
    [2]=> int(100)
    [3]=> int(11)
    [4]=> string(1) "a"
  }
  [1]=> array(5) {
    [0]=> int(1)
    [1]=> int(3)
    [2]=> string(1) "2"
    [3]=> int(2)
    [4]=> int(1)
  }
}

Example #3 Sorting database results

For this example, each element in the data array represents one row in a table. This type of dataset is typical of database records.

Example data:

volume | edition
-------+--------
    67 |       2
    86 |       1
    85 |       6
    98 |       2
    86 |       6
    67 |       7

The data as an array, called data . This would usually, for example, be obtained by looping with mysqli_fetch_assoc() .

<?php
$data[] = array('volume' => 67, 'edition' => 2);
$data[] = array('volume' => 86, 'edition' => 1);
$data[] = array('volume' => 85, 'edition' => 6);
$data[] = array('volume' => 98, 'edition' => 2);
$data[] = array('volume' => 86, 'edition' => 6);
$data[] = array('volume' => 67, 'edition' => 7);
?>

In this example, we will order by volume descending, edition ascending.

We have an array of rows, but array_multisort() requires an array of columns, so we use the below code to obtain the columns, then perform the sorting.

<?php
// Obtain a list of columns
foreach ($data as $key => $row) {
    $volume[$key]  = $row['volume'];
    $edition[$key] = $row['edition'];
}

// you can use array_column() instead of the above code
$volume  = array_column($data, 'volume');
$edition = array_column($data, 'edition');

// Sort the data with volume descending, edition ascending
// Add $data as the last parameter, to sort by the common key
array_multisort($volume, SORT_DESC, $edition, SORT_ASC, $data);
?>

The dataset is now sorted, and will look like this:

volume | edition
-------+--------
    98 |       2
    86 |       1
    86 |       6
    85 |       6
    67 |       2
    67 |       7

Example #4 Case insensitive sorting

Both SORT_STRING and SORT_REGULAR are case sensitive, strings starting with a capital letter will come before strings starting with a lowercase letter.

To perform a case insensitive sort, force the sorting order to be determined by a lowercase copy of the original array.

<?php
$array = array('Alpha', 'atomic', 'Beta', 'bank');
$array_lowercase = array_map('strtolower', $array);

array_multisort($array_lowercase, SORT_ASC, SORT_STRING, $array);

print_r($array);
?>

The above example will output:

Array
(
    [0] => Alpha
    [1] => atomic
    [2] => bank
    [3] => Beta
)

See Also

  • usort() - Sort an array by values using a user-defined comparison function
  • The comparison of array sorting functions
Read article

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