max

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

max — 找出最大值

说明

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

替代签名（不支持命名参数）：

max(array $value_array): mixed

如果仅有一个参数且为数组，max() 返回该数组中最大的值。如果第一个参数是整数、字符串或浮点数，则至少需要两个参数而 max() 会返回这些值中最大的一个。可以比较无限多个值。

注意:
不同类型的值将使用标准比较规则进行比较。例如，一个非数字 string 与 int 比较时就当做是 0，但多个非数字 string 值将会按照字母数字比较。返回的实际值是未应用任何转换的原始类型。

警告

传递不同类型的参数时要小心，因为 max() 会产生不可预测的结果。

参数

value: 任何可比较的值。
values: 任何可比较的值。
value_array: 包含值的数组。

返回值

max() 根据标准比较返回认为是“最大”的参数值。如果不同类型的多个值认为相等（比如 0 与 'abc'），则将会返回提供给函数的第一个值。

错误／异常

如果传递空数组，max() 抛出 ValueError。

更新日志

版本	说明
8.0.0	max() 现在失败时会抛出 ValueError；之前会返回 `false` 并发出 `E_WARNING` 错误。
8.0.0	由于字符串到数字的比较已经改变，max() 在这些情况下不再根据参数的顺序返回不同的值。

示例

示例 #1 使用 max() 的示例

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

// Here we are comparing -1 < 0, so 'hello' is the highest value
echo max('hello', -1);    // hello

// With multiple arrays of different lengths, max returns the longest
$val = max(array(2, 2, 2), array(1, 1, 1, 1)); // array(1, 1, 1, 1)

// Multiple arrays of the same length are compared from left to right
// so in our example: 2 == 2, but 5 > 4
$val = max(array(2, 4, 8), array(2, 5, 1)); // array(2, 5, 1)

// 如果同时给出数组和非数组，则绝对不会返回数组
// 因为比较认为数组大于任何值
$val = max('string', array(2, 5, 7), 42);   // array(2, 5, 7)

// If one argument is NULL or a boolean, it will be compared against
// other values using the rule FALSE < TRUE regardless of the other types involved
// In the below example, -10 is treated as TRUE in the comparison
$val = max(-10, FALSE); // -10

// 0, on the other hand, is treated as FALSE, so is "lower than" TRUE
$val = max(0, TRUE); // TRUE
?>

参见

min() - 找出最小值
count() - 统计数组、Countable 对象中所有元素的数量

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＋添加备注

用户贡献的备注 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;
    }
}
?>