in_array

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

in_array — Checks if a value exists in an array

Description

in_array(mixed $needle, array $haystack, bool $strict = false): bool

Searches for needle in haystack using loose comparison unless strict is set.

Parameters

needle: The searched value.

Note:
If needle is a string, the comparison is done in a case-sensitive manner.
haystack: The array.
strict: If the third parameter strict is set to true then the in_array() function will also check the types of the needle in the haystack.

Note:
Prior to PHP 8.0.0, a string needle will match an array value of 0 in non-strict mode, and vice versa. That may lead to undesireable results. Similar edge cases exist for other types, as well. If not absolutely certain of the types of values involved, always use the strict flag to avoid unexpected behavior.

Return Values

Returns true if needle is found in the array, false otherwise.

Examples

Example #1 in_array() example

<?php
$os = array("Mac", "NT", "Irix", "Linux");
if (in_array("Irix", $os)) {
    echo "Got Irix";
}
if (in_array("mac", $os)) {
    echo "Got mac";
}
?>

The second condition fails because in_array() is case-sensitive, so the program above will display:

Got Irix

Example #2 in_array() with strict example

<?php
$a = array('1.10', 12.4, 1.13);

if (in_array('12.4', $a, true)) {
    echo "'12.4' found with strict check\n";
}

if (in_array(1.13, $a, true)) {
    echo "1.13 found with strict check\n";
}
?>

The above example will output:

1.13 found with strict check

Example #3 in_array() with an array as needle

<?php
$a = array(array('p', 'h'), array('p', 'r'), 'o');

if (in_array(array('p', 'h'), $a)) {
    echo "'ph' was found\n";
}

if (in_array(array('f', 'i'), $a)) {
    echo "'fi' was found\n";
}

if (in_array('o', $a)) {
    echo "'o' was found\n";
}
?>

The above example will output:

'ph' was found
  'o' was found

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User Contributed Notes 6 notes

down

414

beingmrkenny at gmail dot com ¶

13 years ago

Loose checking returns some crazy, counter-intuitive results when used with certain arrays. It is completely correct behaviour, due to PHP's leniency on variable types, but in "real-life" is almost useless.

The solution is to use the strict checking option.

<?php

// Example array

$array = array(
    'egg' => true,
    'cheese' => false,
    'hair' => 765,
    'goblins' => null,
    'ogres' => 'no ogres allowed in this array'
);

// Loose checking -- return values are in comments

// First three make sense, last four do not

in_array(null, $array); // true
in_array(false, $array); // true
in_array(765, $array); // true
in_array(763, $array); // true
in_array('egg', $array); // true
in_array('hhh', $array); // true
in_array(array(), $array); // true

// Strict checking

in_array(null, $array, true); // true
in_array(false, $array, true); // true
in_array(765, $array, true); // true
in_array(763, $array, true); // false
in_array('egg', $array, true); // false
in_array('hhh', $array, true); // false
in_array(array(), $array, true); // false

?>

down

Julian Sawicki ¶

1 year ago

Here is a recursive in_array function: 

<?php

$myNumbers = [
    [1,2,3,4,5],
    [6,7,8,9,10],
];

$array = [
    'numbers' => $myNumbers
];

// Let's try to find number 7 within $array
$hasNumber = in_array(7, $array, true); // bool(false)
$hasNumber = in_array_recursive(7, $array, true); // bool(true)

function in_array_recursive(mixed $needle, array $haystack, bool $strict): bool
{
    foreach ($haystack as $element) {
        if ($element === $needle) {
            return true;
        }

        $isFound = false;
        if (is_array($element)) {
            $isFound = in_array_recursive($needle, $element, $strict);
        }
        
        if ($isFound === true) {
            return true;
        }
    }

    return false;
}

down

rhill at xenu-directory dot net ¶

15 years ago

I found out that in_array will *not* find an associative array within a haystack of associative arrays in strict mode if the keys were not generated in the *same order*:

<?php

$needle = array(
    'fruit'=>'banana', 'vegetable'=>'carrot'
    );

$haystack = array(
    array('vegetable'=>'carrot', 'fruit'=>'banana'),
    array('fruit'=>'apple', 'vegetable'=>'celery')
    );

echo in_array($needle, $haystack, true) ? 'true' : 'false';
// Output is 'false'

echo in_array($needle, $haystack) ? 'true' : 'false';
// Output is 'true'

?>

I had wrongly assumed the order of the items in an associative array were irrelevant, regardless of whether 'strict' is TRUE or FALSE: The order is irrelevant *only* if not in strict mode.

down

leonhard dot radonic+phpnet at gmail dot com ¶

2 years ago

I got an unexpected behavior working with in_array. I'm using following code:

<?php
// ...
$someId = getSomeId(); // it gets generated/fetched by another service, so I don't know what value it will have. P.S.: it's an integer

// The actual data in my edge-case scenario:
// $someId = 0;
// $anyArray = ['dataOne', 'dataTwo'];
if (in_array($someId, $anyArray)) {
    // do some work
}
// ...
?>

With PHP7.4, in_array returns boolean true.
With PHP8.1, in_array returns boolean false.

It took me quite some time to find out what's going on.

down

eurorusty at yahoo dot ca ¶

27 days ago

I'm not sure why PHP doesn't provide a way to specify a binary search. Here's an example of the performance gains, for this array size, about 50x improvement using interpreted PHP. If built in, it could probably achieve around 1000x improvement, again for this array size.

<?php

// Set up sorted array
$X = array(1);
for ($j = 1; $j < 50000; ++$j)
    $X[] = $X[$j - 1] + rand(1, 6);

// Using in_array
$x = -microtime(true);
$m = 0;
for ($j = 0; $j < 10000; ++$j)
    $m += in_array(rand(1, 175000), $X);
$x += microtime(true);
echo $x.PHP_EOL;

// Using binarySearch
$x = -microtime(true);
$m = 0;
for ($j = 0; $j < 10000; ++$j)
    $m += binarySearch($X, rand(1, 175000));
$x += microtime(true);
echo $x.PHP_EOL;

function binarySearch($array, $value) {
    $low = 0;
    $high = count($array) - 1;
    while ($low <= $high) {
        $pivot = floor(($low + $high) / 2);
        if ($array[$pivot] == $value)
            return true;
        if ($value < $array[$pivot])
            $high = $pivot - 1;
        else
            $low = $pivot + 1;
    }
    // No match
    return false;
}

/* Sample outputs, first is in_array, second is binarySearch
1.3544600009918
0.026464939117432

1.6158990859985
0.033976078033447

1.5184400081635
0.026461124420166
*/

down

-4

Armands Rieksti ¶

1 year ago

I'd like to point out that, if you're using Enum data structures and want to compare whether an array of strings has a certain string Enum in it, you need to cast it to a string.

From what I've tested, the function works correctly:
if the array is filled with strings and you're searching for a string;
if the array is filled with Enums and you're searching for an Enum.

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in_array

Description

Parameters

Return Values

Examples

See Also

Found A Problem?

User Contributed Notes 6 notes