max

(PHP 4, PHP 5)

max — 找出最大值

说明

mixed max ( array $values )

mixed max ( mixed $value1 , mixed $value2 [, 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。

Note:

PHP 会将非数值的 string 当成 0，但如果这个正是最大的数值则仍然会返回一个字符串。如果多个参数都求值为 0 且是最大值， max() 会返回其中数值的 0，如果参数中没有数值的 0，则返回按字母表顺序最大的字符串。

参数

values: 包含了多个值的数组。
value1: Any comparable value.
value2: Any comparable value.
...: Any comparable value.

返回值

max() 返回参数中数值最大的值。 If multiple values can be considered of the same size, the one that is listed first will be returned.

When max() is given multiple array s, the longest array is returned. If all the arrays have the same length, max() will use lexicographic ordering to find the return value.

When given a string it will be cast as an integer when comparing.

范例

Example #1 使用 max() 的例子

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

// When 'hello' is cast as integer it will be 0. Both the parameters are equally
// long, so the order they are given in determines the result
 echo  max ( 0 ,  'hello' );      // 0
 echo  max ( 'hello' ,  0 );      // hello

 echo  max ( '42' ,  3 );  // '42'

// Here 0 > -1, so 'hello' is the return value.
 echo  max (- 1 ,  'hello' );     // 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)

// 对多个数组，max 从左向右比较。
   // 因此在本例中：2 == 2，但 4 < 5
 $val  =  max (array( 2 ,  4 ,  8 ), array( 2 ,  5 ,  7 ));  // array(2, 5, 7)

// 如果同时给出数组和非数组作为参数，则总是将数组视为
   // 最大值返回
 $val  =  max ( 'string' , array( 2 ,  5 ,  7 ),  42 );    // array(2, 5, 7)
 ?>

参见

min() - 找出最小值
count() - 计算数组中的单元数目或对象中的属性个数

用户评论:

[#1] ReVo_ [2014-06-12 15:28:52]

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

[#2] volch5 at gmail dot com [2014-05-07 16:07:46]

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

[#3] levim at php dot net [2012-08-22 05:18:27]

<?php 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 [2012-05-07 18:42:58]

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; } } ?>

[#5] costinu [2012-02-02 06:21:16]

max(null, 0) = null
max(0, null) = 0

[#6] sun at drupal dot org [2011-08-03 11:25:03]

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.

[#7] php at rijkvanwel dot nl [2011-04-12 02:08:00]

To get the largest key in an array:

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

[#8] Alex Stanhope [2010-10-28 03:00:55]

If you want to test whether x lies within two bounds:

<?php static function isInRange($x, $y1, $y2) { return( ($x >= min($y1, $y2)) && ($x <= max($y1, $y2)) ); } //called by: class::isInRange(10,12,2); //or $this->isInRange(10,12,2); //or (drop static) isInRange(10,12,2); //simple test function: static function unit_isInRange() { $output = array(); $inputlist[] = array(10, 12, 2, true); $inputlist[] = array(13, 12, 2, false); $inputlist[] = array(2, -2, 2, true); $inputlist[] = array(2, -8, -2, false); foreach($inputlist as $input) { $output[] = array( 'input' => array($input[0], $input[1], $input[2]), 'output' => self::isInRange($input[0],$input[1],$input[2]), 'expected' => $input[3], ); } return($output); } ?>

[#9] Alex Rath [2010-04-10 11:27:28]

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 ?>

[#10] grillen at abendstille dot at [2010-04-02 03:55:18]

max only accepts not empty arrays.

if you work a lot with numerical arrays and with max, this function may come in handy:

<?php if (!function_exists('emax')) { function emax($arr) { if (!is_array($arr)) return call_user_func_array('max', func_get_args()); if (count($arr) == 0) return 0; return max($arr); } } ?>

[#11] marcini [2009-05-11 07:34:29]

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.

[#12] ries at vantwisk dot nl [2008-11-09 06:36:58]

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

[#13] Marcus Zacco [2008-09-29 09:47:23]

This code loops through seven arrays and finds the highest average value within those arrays - and changes the font color for it. Great for highlighting.

The biggest take-away is this the row
if($average[$i] == max($average))

The number_format just rounds the numbers to 0 decimal points.

<?php for ( $i = 0; $i <= 6; $i++) { $num = $i+1; if($average[$i] == max($average)) { echo "Value ".$num.": <font color='red'>".number_format($average[$i], 0, '.', '')." % </font<br>"; } else { echo "Value ".$num.": ".number_format($average[$i],0,'.','')." %<br>"; } } ?>

### OUTPUT

Value 1: 52 %
Value 2: 58 %
Value 3: 56 %
Value 4: 73 %
Value 5: 77 % <- this 77 is highlighted in red
Value 6: 71 %
Value 7: 75 %

[#14] harmor [2008-02-21 09:56:08]

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

[#15] michaelangel0 at mail.com [2007-07-04 15:00:34]

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); } ?>

[#16] jeremi23 at gmail dot com [2007-06-14 03:09:59]

max on a an array with key/values

<?php $tmp = array(1 => 5, 2=> 3); echo max($tmp); ?>

this return 5, so the max is done on the values.

[#17] johnmott59 at hotmail dot com [2007-05-17 12:35:22]

To find the maximum value from a set of 1-dimensional arrays, do this:

<?php $d1 = array(450,420,440,430,421); $d2 = array(460,410,410,430,413,375,256,411,656); $d3 = array(430,440,470,435,434,255,198); $t = max(max($d1),max($d2),max($d3)); // $t is 656 ?>

The inner max() functions operate on the arrays, the outer max compares the numeric results of the inner ones.

[#18] johnphayes at gmail dot com [2006-05-02 09:27:26]

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