Math 函数
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max

(PHP 4, PHP 5)

max — 找出最大值

说明

mixed max ( number $arg1 , number $arg2 )
mixed max ( array $numbers [, array $... ] )

max() 返回参数中数值最大的值。

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。

Example #1 使用 max() 的例子

<?php
echo max(1, 3, 5, 6, 7);  // 7
echo max(array(2, 4, 5)); // 5
echo max(0, 'hello');     // 0
echo max('hello', 0);     // hello
echo max(-1, 'hello');    // hello

// 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() 和 count()。

Math 函数
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PHP手册
PHP手册 - N: 找出最大值

用户评论:

costinu (02-Feb-2012 02:21)

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

sun at drupal dot org (03-Aug-2011 07:25)

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.

php at rijkvanwel dot nl (12-Apr-2011 10:08)

To get the largest key in an array:

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

Alex Stanhope (28-Oct-2010 11:00)

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);
    }
?>

dan at coders dot co dot nz (23-May-2010 07:29)

max() on undefined parameters does not assume the value is zero, it ignores it.
<?php
$dimensions = array('left' => -2);
// If $dimensions['right'] was never set,
// we may expect it to be treated as zero, but
print max($dimensions['left'], $dimensions['right']);
//
// Returns -2, not zero

print max(0+$dimensions['left'], 0+$dimensions['right']);
?>
would be a work-around, but it's probably tidier to ensure your values are set correctly first.

(on PHP 5.2.11 anyway)

Alex Rath (10-Apr-2010 07:27)

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

?>

grillen at abendstille dot at (02-Apr-2010 11:55)

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);
    }
}
?>

artem dot yagutyan at gmail dot com (27-Mar-2010 11:28)

This Is Good Example: For max to min

<?php

function max_key($array) {
foreach ($array as $key => $val) {
    if ($val == max($array)) return $key;
    }
}

$array = array(10, 2, 5, 7, 4,15,32,8,41,25);
$array_count=count($array);   
for($i=1;$i<=$array_count;$i++){
    $max_val[$i]=max_key($array);
   
    $view=$array[$max_val[$i]];
       
    unset($array[$max_val[$i]]);
       
       
    print $view."<br />"; //
}

/* OUTPUT
41 // Max
32
25
15
10
8
7
5
4
2 //Min
*/

?>

marcini (11-May-2009 03:34)

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.

ries at vantwisk dot nl (09-Nov-2008 02:36)

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

Marcus Zacco (29-Sep-2008 05:47)

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 %

harmor (21-Feb-2008 05:56)

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

michaelangel0 at mail.com (04-Jul-2007 11:00)

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);
}
?>

jeremi23 at gmail dot com (14-Jun-2007 11:09)

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.

johnmott59 at hotmail dot com (17-May-2007 08:35)

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.

johnphayes at gmail dot com (02-May-2006 05:27)

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