# max

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

max找出最大值

### 说明

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

max(array `\$value_array`): mixed

### 参数

`value`

`values`

`value_array`

### 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``'abc'`），则将会返回提供给函数的第一个值。

### 更新日志

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

`<?phpecho max(2, 3, 1, 6, 7); // 7echo max(array(2, 4, 5)); // 5// Here we are comparing -1 < 0, so 'hello' is the highest valueecho 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

### User Contributed Notes 20 notes

67
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?>`
Samu
9 months ago
`With modern PHP versions supporting the array spread operator for function arguments, it's tempting to call max() like this:<?phpfunction 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:<?phpfunction 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.`
16
deoomen
2 years ago
`Watch out after PHP 8.0!Sample code:<?phpecho max(0,'hello');?>Before PHP 8.0 will return int(0) but since PHP 8.0 above code returns string("hello")!!`
21
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+00:00echo min(\$dt1,\$dt2)->format(DateTime::RFC3339) . PHP_EOL; // 2014-05-07T18:53:00+03:00?>It works at least 5.3.3-7+squeeze17`
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)=true2. max(true,0)=true3. max(100,true)=1004. max(false,100)=1005. max(100,false)=1006. min(true,100)=true7. min(true,0)=08. min(100,true)=1009. min(false,100)=false10. min(100,false)=false11. min(true,false)=false12. max(true,false)=true`
14
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?>`
ries at vantwisk dot nl
15 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`
17
costinu
12 years ago
```max(null, 0) = null max(0, null) = 0```
10
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"<?phpfunction 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`
10
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.`
info at osworx dot net
5 years ago
`Be aware if a array like this is used (e.g. values from a shopping cart):<?phpArray( [0] => 142,80 [1] => 39,27 [2] => 22,80 [3] => 175,80)?>The result will be: 39,27 and not - as expected - 175,80So, to find the max value, use integer only like:<?phpArray( [0] => 14280 [1] => 3927 [2] => 2280 [3] => 17580)?>and you will get the correct result: 17580`
blackmac01 at gmail dot com
4 years ago
`In response to: keith at bifugi dot comIf 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 valueforeach(\$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.`
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?>`
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); } ?>```
sun at drupal dot org
12 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.`
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```
-3
levim at php dot net
11 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.`
-4
toon dot baeyens at gmail dot com
12 years ago
`A little function for multi-dimensional arrays:<?phpfunction amax(\$array){ if(is_array(\$array)){ foreach(\$array as \$key => \$value){ \$array[\$key] = amax(\$value); } return max(\$array); }else{ return \$array; }}?>`
-5
chris at candm dt org dt uk
3 years ago
`A function to return the key of the max value of an array. For multiple max values, it will return the key of first. Change > to >= to get the last.function array_max_key(\$arr) { \$maxkey=''; \$maxval=false; array_walk(\$arr, function (&\$cval,&\$ckey) use(&\$maxkey,&\$maxval) { if (\$maxval === false || \$cval > \$maxval) { \$maxval = \$cval; \$maxkey = \$ckey; } } ); return \$maxkey;}`
-9
Michael Blinn
5 years ago
`Be careful using max() with objects, as it returns a reference not a new object.<?php\$min_date = date_create('2019-03-05');\$max_date = date_create('2019-03-06');\$date_by_reference = max(\$min_date, \$max_date);// \$date_by_reference and \$max_date are now the same objectecho '\$max_date is ' . date_format(\$max_date, 'Y-m-d') . PHP_EOL; // '2019-03-06'echo '\$date_by_reference is ' . date_format(\$date_by_reference, 'Y-m-d') . PHP_EOL; // '2019-03-06'date_add(\$date_by_reference, date_interval_create_from_date_string('1 days')); // Add 1 day to \$date_by_reference, changes \$max_date tooecho '\$max_date is changed ' . date_format(\$max_date, 'Y-m-d') . PHP_EOL; // '2019-03-07'echo '\$date_by_reference is changed ' . date_format(\$date_by_reference, 'Y-m-d') . PHP_EOL; // '2019-03-07'?>`