max

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

max — 最大値を返す

説明

max(mixed $value, mixed ...$values): mixed

代替のシグネチャ (名前付き引数をサポートしていません):

max(array $value_array): mixed

パラメータとして配列をひとつだけ渡した場合は、max() は配列の中で最も大きい数値を返します。ふたつ以上のパラメータを指定した場合は、max() はそれらの中で最も大きいものを返します。

注意:
異なる型の値を比較する際には、標準の比較ルールに従います。たとえば、数値形式でない string を int と比較するときには、数値 0 と評価します。しかし、数値形式でない string どうしを比較するときには、アルファベット順で評価します。返される値は、何も変換をしていない、元の型の値となります。

警告

異なる型の値を引数として渡す際には注意しましょう。 max() が予期せぬ結果を返す可能性があるからです。

パラメータ

value: 任意の比較可能な値。
values: 任意の比較可能な複数の値。
value_array: 値を含んだ配列。

戻り値

max() は、パラメータとして渡した値の中で、標準の比較ルールに従って最大になるものを返します。異なる型で同じ値と評価される複数の値 (0 と 'abc' など) があった場合は、関数に最初に渡されたほうを返します。

エラー / 例外

max() に空の配列を渡すと、 ValueError をスローします。

変更履歴

バージョン	説明
8.0.0	max() は失敗した場合に、 ValueError をスローするようになりました。これより前のバージョンでは、`false` を返し、 `E_WARNING` レベルのエラーが発生していました。
8.0.0	文字列と数値の比較方法が変更されたため、数値と非数値文字列を比較した場合に、引数の順番に応じて異なる値を返さなくなりました。

例

例1 max() の使用例

<?php
echo max(2, 3, 1, 6, 7);  // 7
echo max(array(2, 4, 5)); // 5

// -1 と 0 の比較なので、'hello' のほうが大きくなります
echo max('hello', -1);    // hello

// 長さが異なる複数の配列を渡すと、いちばん長い配列を返します
$val = max(array(2, 2, 2), array(1, 1, 1, 1)); // array(1, 1, 1, 1)

// 同じ長さの複数の配列を渡すと、max はその要素を左から
// 辞書順に比較します。この例では 2 == 2 ですが 5 > 4 となります
$val = max(array(2, 4, 8), array(2, 5, 1)); // array(2, 5, 1)

// 配列と配列でない値が渡された場合、常に
// 配列が最大と判定されます。
$val = max('string', array(2, 5, 7), 42);   // array(2, 5, 7)

// 一方の値が NULL や boolean の場合、それを他の値と比較するときには、
// もう一方の値の型が何であるかにかかわらず、FALSE < TRUE というルールを使います。
// 以下の例では、-10 は TRUE と評価されます。
$val = max(-10, FALSE); // -10

// 一方 0 は FALSE と評価されるので、TRUE よりは小さいとみなされます。
$val = max(0, TRUE); // TRUE
?>

参考

min() - 最小値を返す
count() - 配列または Countable オブジェクトに含まれるすべての要素の数を数える

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User Contributed Notes 18 notes

down

keith at bifugi dot com ¶

8 years ago

The simplest way to get around the fact that max() won't give the key is array_search:

<?php
$student_grades = array ("john" => 100, "sarah" => 90, "anne" => 100);
$top_student = array_search(max($student_grades),$student_grades); // john
?>

This could also be done with array_flip, though overwriting will mean that it gets the last max value rather than the first:

<?php
$grades_index = array_flip($student_grades);
$top_student = $grades_index[max($student_grades)]; // anne
?>

To get all the max value keys:

<?php
$top_students = array_keys($student_grades,max($student_grades)); // john, anne
?>

down

Samu ¶

1 year ago

With modern PHP versions supporting the array spread operator for function arguments, it's tempting to call max() like this:

<?php
function stuff(): iterable {
    // This function might yield 0, 1 or n values.
}

$foo = max(...stuff());
?>

However, this is dangerous if you cannot guarantee that your generator yields **minimum** two values.

The gotcha here is that when max() receives a single argument, it must be an array of values. (When the generator doesn't yield any values, max() will throw an ArgumentCountError.)

If you can guarantee that your generator yields at least one value, then it's safe to call max by relying on the aforementioned array expectation:

<?php
function stuff(): iterable {
    // This function will yield 1...n values.
}

// Note that here the generator is first read into an array.
$foo = max([...stuff()]);
?>

If the array is empty, max() will throw a ValueError.

The added burden is that faulty code could appear to appear to function just fine but fails at random, probably causing a lot of head-scratching at first.

down

deoomen ¶

2 years ago

Watch out after PHP 8.0!

Sample code:

<?php
echo max(0,'hello');
?>

Before PHP 8.0 will return int(0) but since PHP 8.0 above code returns string("hello")!!

down

volch5 at gmail dot com ¶

10 years ago

max() (and min()) on DateTime objects compares them like dates (with timezone info) and returns DateTime object.
<?php 
$dt1 = new DateTime('2014-05-07 18:53', new DateTimeZone('Europe/Kiev'));
$dt2 = new DateTime('2014-05-07 16:53', new DateTimeZone('UTC'));
echo max($dt1,$dt2)->format(DateTime::RFC3339) . PHP_EOL; // 2014-05-07T16:53:00+00:00
echo min($dt1,$dt2)->format(DateTime::RFC3339) . PHP_EOL; // 2014-05-07T18:53:00+03:00
?>

It works at least 5.3.3-7+squeeze17

down

Alex Rath ¶

14 years ago

Notice that whenever there is a Number in front of the String, it will be used for Comparison.

<?php

  max('7iuwmssuxue', 1); //returns 7iuwmssuxu
  max('-7suidha', -4); //returns -4

?>

But just if it is in front of the String

<?php

  max('sdihatewin7wduiw', 3); //returns 3

?>

down

johnphayes at gmail dot com ¶

18 years ago

Regarding boolean parameters in min() and max():

(a) If any of your parameters is boolean, max and min will cast the rest of them to boolean to do the comparison.
(b) true > false
(c) However, max and min will return the actual parameter value that wins the comparison (not the cast).

Here's some test cases to illustrate:

1.  max(true,100)=true
2.  max(true,0)=true
3.  max(100,true)=100
4.  max(false,100)=100
5.  max(100,false)=100
6.  min(true,100)=true
7.  min(true,0)=0
8.  min(100,true)=100
9.  min(false,100)=false
10. min(100,false)=false
11. min(true,false)=false
12. max(true,false)=true

down

costinu ¶

12 years ago

max(null, 0) = null

max(0, null) = 0

down

ries at vantwisk dot nl ¶

16 years ago

I had several occasions that using max is a lot slower then using a if/then/else construct. Be sure to check this in your routines!

Ries

down

ReVo_ ¶

10 years ago

Sometimes you could need to get the max from an array which looks like this:

<?php
$arrTest = array(
    array( "day" => 1, "b" => 10 ),
    array( "day" => 2, "b" => 43 ),
    array( "day" => 3, "b" => 2 ),
    array( "day" => 4, "b" => -3 ),
    array( "day" => 5, "b" => 4 ),
    array( "day" => 6, "b" => -5 )
);
?>
all max functions i see around don't provide a way to get the max value of the values in (example) key "b"

<?php
function maxValueInArray($array, $keyToSearch)
{
    $currentMax = NULL;
    foreach($array as $arr)
    {
        foreach($arr as $key => $value)
        {
            if ($key == $keyToSearch && ($value >= $currentMax))
            {
                $currentMax = $value;
            }
        }
    }

    return $currentMax;
}

//                                            array       key
$value = maxValueInArray($arrTest, "b");

?>

output: 43

down

marcini ¶

15 years ago

Note that max() can compare dates, so if you write something like this:

<?php
$dates = array('2009-02-15', '2009-03-15');
echo max($dates);
?>

you will get: 2009-03-15.

down

php at rijkvanwel dot nl ¶

13 years ago

To get the largest key in an array:

<?php
$array = array( 0 => 'first', 1=> 'second', /* ... */ 99 => 'nth' );
$max_key = max( array_keys( $array ) ); // 99
?>

down

info at osworx dot net ¶

5 years ago

Be aware if a array like this is used (e.g. values from a shopping cart):
<?php
Array
(
    [0] => 142,80
    [1] => 39,27
    [2] => 22,80
    [3] => 175,80
)?>
The result will be: 39,27 and not - as expected - 175,80

So, to find the max value, use integer only like:
<?php
Array
(
    [0] => 14280
    [1] => 3927
    [2] => 2280
    [3] => 17580
)?>
and you will get the correct result: 17580

down

blackmac01 at gmail dot com ¶

5 years ago

In response to: keith at bifugi dot com

If you want to find the specific key(s) that match the maximum value in an array where the values may be duplicated, you can loop through and perform a simple check:
<?php

# Example Array
$a = array(
     'key1' => 100,
     'key2' => 90,
     'key3' => 100,
     'key4' => 90,
);

# First get the maximum value
$max = max($a);

# Create a new array containing all keys which have the max value
foreach($a as $key => $val) {     
     if($val === $max) $b[] = $key;
}

# If you want a string list, just do this
$b = implode(' ', $b);
?>

This produces consistent results and will scale well in terms of performance, whereas functions like array_search and array_flip can lead to degraded performance when dealing with large amounts of data.

down

michaelangel0 at mail.com ¶

17 years ago

Matlab users and others may feel lonely without the double argument output from min and max functions.



To have the INDEX of the highest value in an array, as well as the value itself, use the following, or a derivative:



<?php

function doublemax($mylist){

  $maxvalue=max($mylist);

  while(list($key,$value)=each($mylist)){

    if($value==$maxvalue)$maxindex=$key;

  }

  return array("m"=>$maxvalue,"i"=>$maxindex);

}

?>

down

sun at drupal dot org ¶

13 years ago

Note that max() throws a warning if the array is empty:

<?php
$a = array();
max($a);
// Warning: max(): Array must contain at least one element
?>

So make sure your data isn't empty.

down

-1

harmor ¶

16 years ago

A way to bound a integer between two values is:



<?php

function bound($x, $min, $max)

{

     return min(max($x, $min), $max);

}

?>



which is the same as:



<?php

$tmp = $x;

if($tmp < $min)

{

    $tmp = $min;

}

if($tmp > $max)

{

     $tmp = $max;

}

$y = $tmp;

?>



So if you wanted to bound an integer between 1 and 12 for example:



Input:

<?php

$x = 0;

echo bound(0, 1, 12).'<br />';

$x = 1;

echo bound($x, 1, 12).'<br />';

$x = 6;

echo bound($x, 1, 12).'<br />';

$x = 12;

echo bound($x, 1, 12).'<br />';

$x = 13;

echo bound($x, 1, 12).'<br />';

?>



Output:

1

1

6

12

12

down

-4

levim at php dot net ¶

12 years ago

<?php
/**
 * @param array $array
 *
 * @return int|null Returns the largest value of the array. Returns NULL if no 
 *     integers are found.
 */
function array_max_recursive(array $array) {
    $max = NULL;
    $stack = array($array);

    do {
        $current = array_pop($stack );
        foreach ($current as $value) {
            if (is_array($value)) {
                $stack[] = $value;
            } elseif (filter_var($value, FILTER_VALIDATE_INT) !== FALSE) {
                // max(NULL, 0) returns NULL, so cast it
                $max = (int) max($max, $value);
            }
        }

    } while (!empty($stack));

    return $max;
}
?>

 - This function is not actually recursive, but fulfills the requirement that it works on sub-arrays.  I do this because PHP is not very good at recursion.  I also did it because I enjoy doing things this way.  
 - It returns something of type int, never a string representation of an int. The exception is when you provide an array that does not contain any integers.  It will then return NULL.
 - It ignores non-array, non-int values.

down

-5

toon dot baeyens at gmail dot com ¶

12 years ago

A little function for multi-dimensional arrays:
<?php
function amax($array){
    if(is_array($array)){
        foreach($array as $key => $value){
            $array[$key] = amax($value);
        }
        return max($array);
    }else{
        return $array;
    }
}
?>

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