Question

我正在使用我的sql表中的二维数据的欧几里德距离公式实现k-最近邻alog。事情看起来还不错，即使它表现出奇怪的行为。

代码：

    $result1 = mysqli_query($con,"SELECT pcount, ncount from test");
    $result2 = mysqli_query($con,"SELECT pcount, ncount from test");
    $i = 0;
    $min = 0;
    while ($row1 = @mysqli_fetch_array($result1))
    {
        $pcount = $row1['pcount'];
        $ncount = $row1['ncount'];
        echo "pcount is $pcount<br/>";
        echo "ncount is $ncount<br/></br>";
        $a[$i] = $pcount ;
        $b[$i] = $pcount ;
        $j = 0;
        while ($row2 = @mysqli_fetch_array($result2))
        {
            echo "j is $j <br/>";
            $a[$j] = $row2['pcount'];   
            $b[$j] = $row2['ncount'];
            $diff = sqrt(($a[$i] - $a[$j])^2 + ($b[$i] - $b[$j])^2 );
        $j= $j + 1;
        echo "$diff <br>";
        }               
        echo "i is $i <br/>";
                $i = $i + 1;    
    }

它给出了这个结果：

j is 0 
Difference : 0 
j is 1 
Difference : 1.4142135623731 
j is 2 
Difference : 0 
j is 3 
Difference : 0 
j is 4 
Difference : 1.4142135623731 
j is 5 
Difference : 1.4142135623731 
j is 6 
Difference : 1.4142135623731 
i is 0

在表格中我总共有8行，但上面的结果只有7行。为什么呢？

首先对$i = 0 on执行while循环，其余i = 1到7无操作。有人可以告诉我什么是虫子吗？

表中的数据是

pcount  ncount
20  80
21  79
20  80
21  79
19  81
20  80
20  80
20  80

fallens回答后的结果：

j is 0 
Difference : 0 
j is 1 
Difference : NAN 
j is 2 
Difference : 0 
j is 3 
Difference : NAN 
j is 4 
Difference : 1.4142135623731 
j is 5 
Difference : 0 
j is 6 
Difference : 0 
j is 7 
Difference : 0 
i is 0 
pcount is 21
ncount is 79

i is 1 
pcount is 20
ncount is 80

i is 2 
pcount is 21
ncount is 79

i is 3 
pcount is 19
ncount is 81

i is 4 
pcount is 20
ncount is 80

i is 5 
pcount is 20
ncount is 80

i is 6 
pcount is 20
ncount is 80

i is 7

Answer 1

您在内部和外部循环中使用相同的变量。在这两个循环中为row和result s尝试不同的变量名称。与result1一样，row1表示外部result2，row2表示内部循环

它显示7行而不是8行，因为result的第一行已被外环拾取

试试这段代码：

$result1 = mysqli_query($con,"SELECT pcount, ncount from test");
$i = 0;
$min = 0;
while ($row1 = @mysqli_fetch_array($result1))
{
    $pcount = $row1['pcount'];
    $ncount = $row1['ncount'];
    echo "pcount is $pcount<br/>";
    echo "ncount is $ncount<br/></br>";
    $a[$i] = $pcount ;
    $b[$i] = $pcount ;
    $j = 0;

    $result2 = mysqli_query($con,"SELECT pcount, ncount from test");

    while ($row2 = @mysqli_fetch_array($result2))
    {
        echo "j is $j <br/>";
        $a[$j] = $row2['pcount'];   
        $b[$j] = $row2['ncount'];
        $diff = ($a[$i] - $a[$j])^2 + ($b[$i] - $b[$j])^2;
        if( $diff != 0)
        $diff = sqrt( $diff );
    $j= $j + 1;
    echo "$diff <br>";
    }               
    echo "i is $i <br/>";
            $i = $i + 1;    
}

注意为避免NaN，请确保($a[$i] - $a[$j])^2 + ($b[$i] - $b[$j])^2不会产生0。

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