(PHP 4, PHP 5, PHP 7, PHP 8)
in_array — 配列に値があるかチェックする
haystack 内の needle を検索します。
strict が設定されていない限りは型の比較は行いません。
needle探す値。
注意:
needleが文字列の場合、 比較の際に大文字小文字は区別されます。
haystack配列。
strict
三番目のパラメータ strict が
true に設定された場合、
in_array() は、haystack
の中の needle の
型も確認します。
注意:
PHP 8.0.0 より前のバージョンでは、 strict フラグが指定されていない場合に、 配列の値が
0の場合でも文字列にマッチしてしまっていました。逆も同じです。 これにより、望ましくない結果が生じる可能性があります。 似たようなエッジケースは他の型でも存在します。 値の型が完全にわからない場合には、 予期せぬ振る舞いを避けるために常にstrictフラグを使うようにして下さい。
例1 in_array() の例
<?php
$os = array("Mac", "NT", "Irix", "Linux");
if (in_array("Irix", $os)) {
echo "Got Irix";
}
if (in_array("mac", $os)) {
echo "Got mac";
}
?>二番目の条件式は失敗します。in_array() は大文字小文字を区別するからです。したがって次のような出力になります。
Got Irix
例2 strict を指定した in_array() の例
<?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";
}
?>上の例の出力は以下となります。
1.13 found with strict check
例3 needleが配列の場合の in_array()
<?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";
}
?>上の例の出力は以下となります。
'ph' was found 'o' was found
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
?>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;
}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
*/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.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.