PHP数组奇怪的有关问题

$arr1里面是从数据库里取出来的数据，print_r出来如下：
Array
(
    [0] => 30544
    [1] => 30544
    [2] => 30532
    [3] => 30550
    [4] => 30544
    [5] => 30544
    [6] => 30532
    [7] => 30532
    [8] => 30532
    [9] => 30550
    [10] => 30544
    [11] => 30544
    [12] => 30544
    [13] => 30544
    [14] => 30544
    [15] => 30544
    [16] => 30532
    [17] => 30532
    [18] => 30532
    [19] => 30532
)

$arr2 = array('1','2','4','5');

//我用同一个函数 max()取最大值，结果如下：

//arr1的结果，会报错，但是可以取到数据
30550
A PHP Error was encountered

Severity: Warning

Message: max() [function.max]: When only one parameter is given, it must be an array

Filename: test.php

Line Number: 104


//arr2正常，

logminMath 函数
PHP Manual

--------------------------------------------

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

 

参见 min() 和 count()。 

User Contributed Notes
sun at drupal dot org 03-Aug-2011 11:25 
Note that max() throws a warning if the array is empty:



So make sure your data isn't empty. 
php at rijkvanwel dot nl 12-Apr-2011 02:08 
To get the largest key in an array:

 'first', 1=> 'second', /* ... */ 99 => 'nth' );
$max_key = max( array_keys( $array ) ); // 99
?> 
Alex Stanhope 28-Oct-2010 03:00 
If you want to test whether x lies within two bounds: 

= 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 22-May-2010 11:29 
max() on undefined parameters does not assume the value is zero, it ignores it. 
 -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 11:27 
Notice that whenever there is a Number in front of the String, it will be used for Comparison.



But just if it is in front of the String

 
grillen at abendstille dot at 02-Apr-2010 03:55 
max only accepts not empty arrays. 

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

 
artem dot yagutyan at gmail dot com 27-Mar-2010 03:28 
This Is Good Example: For max to min

 $val) {
    if ($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."
"; // 
}

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

?> 
marcini 11-May-2009 07:34 
Note that max() can compare dates, so if you write something like this:



you will get: 2009-03-15. 
ries at vantwisk dot nl 09-Nov-2008 06:36 
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 09:47 
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. 

".number_format($average[$i], 0, '.', '')." % "; 
  } else { 
    echo "Value ".$num.": ".number_format($average[$i],0,'.','')." %
"; 
  } 
} 
?> 

### 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 09:56 
A way to bound a integer between two values is: 

 

which is the same as: 

 $max) 
{ 
     $tmp = $max; 
} 
$y = $tmp; 
?> 

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

Input: 
'; 
$x = 1; 
echo bound($x, 1, 12).'
'; 
$x = 6; 
echo bound($x, 1, 12).'
'; 
$x = 12; 
echo bound($x, 1, 12).'
'; 
$x = 13; 
echo bound($x, 1, 12).'
'; 
?> 

Output: 
1 
1 
6 
12 
12 
michaelangel0 at mail.com 04-Jul-2007 03:00 
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: 

$maxvalue,"i"=>$maxindex); 
} 
?> 
jeremi23 at gmail dot com 14-Jun-2007 03:09 
max on a an array with key/values 

 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 12:35 
To find the maximum value from a set of 1-dimensional arrays, do this: 

 

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 09:27 
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 

--------------------------------------------

logminMath 函数
PHP Manual