我一直在努力从PHP移植到Javascript的变异系数方程,但似乎不能让它工作。
原PHP脚本:
// define variables, strip spaces
$weights = $_POST['weights'];
// define coefficient of variation function
function cv($array){
$n = 0;
$mean = 0;
$M2 = 0;
foreach($array as $x){
if ($x != NULL AND $x != '') {
$n++;
$delta = $x - $mean;
$mean = $mean + $delta/$n;
$M2 = $M2 + $delta*($x - $mean);
$total = $total + $x;
}
}
return (((sqrt($M2/($n - 1))) / ($total/$n))*100);
}
$cv = (cv($weights));
这基本上是一个数组,并计算出它的变异系数。现在我尝试通过Jquery函数将其转换为Javascript:
var fields = $('#cvform').serializeArray();
var count = 0;
var num = 0;
var mean = 0;
var m2 = 0;
var total = 0;
var delta = 0;
jQuery.each(fields, function(i, field){
if (field.value > 0) {
num++;
delta=(field.value-mean);
mean=(mean+delta/num);
m2=(m2+delta*(field.value-mean));
total=(total+field.value);
};
});
var cov=(((Math.sqrt(m2/(num-1)))/(total/num))*100);
$("<span>Coefficient of Variation: " + cov + "</span>").appendTo('#cvdisplay');
虽然javascript函数输出一个答案,但它是不正确的。如果我输入值"3,3,2,3,3,4",PHP脚本给出的输出是21.08,这是正确的。javascript函数给我的值是0.0011418432035849642。
谁能指出方程的不同之处?
您需要通过parseFloat()
(或整数,parseInt()
,任何适合您的)将数组值转换为浮点数:
var fields = $('#cvform').serializeArray();
var count = 0;
var num = 0;
var mean = 0;
var m2 = 0;
var total = 0;
var delta = 0;
$.each(fields, function(i, field) {
alert(field.value);
if (parseFloat(field.value) > 0) {
num++;
delta = (parseFloat(field.value) - mean);
mean = (mean + delta / num);
m2 = (m2 + delta * (parseFloat(field.value) - mean));
total = (total + parseFloat(field.value));
}
});
var cov = (((Math.sqrt(m2 / (num - 1))) / (total / num)) * 100);
$("<span>Coefficient of Variation: " + cov + "</span>").appendTo('#cvdisplay');
问题是javascript行total=(total+field.value);
,结果是0332334
而不是预期的18。正在应用字符串连接而不是数字加法。
可以通过解析整数值来解决这个问题:total += parseInt(field.value);
function stDeviation(array){
var L= array.length,
mean= array.reduce(function(a, b){
return a+b;
})/L,
dev= array.map(function(itm){
var tem= itm-mean;
return tem*tem;
});
return Math.sqrt(dev.reduce(function(a, b){
return a+b;
})/L);
}
Math.mean= function(array){
return array.reduce(function(a, b){ return a+b; })/array.length;
}
Math.stDeviation=function(array){
var mean= Math.mean(array);
dev= array.map(function(itm){return (itm-mean)*(itm-mean); });
return Math.sqrt(dev.reduce(function(a, b){ return a+b; })/array.length);
}
var A2= [6.2, 5, 4.5, 6, 6, 6.9, 6.4, 7.5];
alert ('mean: '+Math.mean(A2)+'; deviation: '+Math.stDeviation(A2))
在这里,我稍微改变了一下代码并使其工作。我基本上把这些部分分开了一点。让它更直接。
<?php
$weights = Array(3,3,2,3,3,4);
// define coefficient of variation function
function cv($array) {
$n = 0;
$mean = 0;
$M2 = 0;
$total = 0;
foreach($array as $x) {
if ( !empty($x) ) {
$n++;
$delta = $x - $mean;
$mean = $mean + $delta / $n;
$M2 = $M2 + $delta * ($x - $mean);
$total = $total + $x;
}
}
$sqrt = sqrt( $M2 / ($n - 1) );
$tn = $total / $n;
echo "Sqrt is $sqrt tn is $tn";
return ( $sqrt / $tn ) * 100;
}
$cv = cv($weights);
?>
<html>
<head>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js"></script>
<script type="text/javascript">
$(document).ready(function() {
var fields = Array(3,3,2,3,3,4);
var count = 0;
var n = 0;
var mean = 0;
var m2 = 0;
var total = 0;
var delta = 0;
jQuery.each(fields, function(i, field) {
//var x = field.value;
var x = 1 * field;
if (x > 0) {
n++;
delta = (x - mean);
mean = (mean + (delta / n));
m2 = (m2 + delta * (x - mean));
total = (total + x);
};
});
var sqrt = Math.sqrt(m2 / (n - 1));
var tn = total / n;
var cov = ((sqrt / tn) * 100);
console.log("Total is: "+ total);
console.log("Sqrt is " + sqrt + " tn is " + tn + " cov is " + cov);
$('#js').text("JS Output is: " + cov);
});
</script>
</head>
<body>
<div>
<div>PHP Output: <?=$cv;?></div>
<div id="js"></div>
</div>
</body>
</html>
下面是您提供的函数的直接翻译。您必须传入一个javascript数字数组,它会生成您正在寻找的结果(至少根据用Node.js编写的单元测试)。您应该在另一个函数中进行类型转换(字符串到数组),以分离您的关注点,并使代码更容易理解;
var CoV = function(ary) {
var mean = 0,
n = 0,
m2 = 0,
total = 0,
delta;
for(var i = 0, l = ary.length; i < l; i += 1) {
n += 1;
delta = ary[i] - mean;
mean = mean + delta / n;
m2 = m2 + delta * (ary[i] - mean)
total = total + ary[i]
}
console.log(mean);
console.log(m2);
console.log(total);
return ((Math.sqrt(m2/(i - 1))) / (total / i)) * 100;
};