# Converting math equation from PHP to Javascript (Jquery)

I’ve been working on getting a Coefficient of Variation equation ported from PHP to Javascript, but can’t seem to get it working.Original PHP script:// define variables, strip spaces\$weights = \$_POST[‘weights’];// define coefficient of variation functionfunction cv(\$array) \$n = 0; \$mean = 0; \$M2 = 0; foreach(\$array as \$x) if (\$x != NULL AND \$x != ”) \$n++; \$delta …

## Converting math equation from PHP to Javascript (Jquery)

I’ve been working on getting a Coefficient of Variation equation ported from PHP to Javascript, but can’t seem to get it working.
Original PHP script:
// 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));This basically takes an array, and figures out the coefficient of variation for it. Now as I try to convert it to Javascript via some Jquery function:
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);
\$(“Coefficient of Variation: ” + cov + ““).appendTo(‘#cvdisplay’);While the javascript function outputs an answer, it is not correct. If I enter the values “3,3,2,3,3,4″ the PHP script gives an output of 21.08, which is correct. The javascript function gives me the value of 0.0011418432035849642.
Can anyone point me to where the equations are differing?

You need to convert your array values to floats via parseFloat() (or integers, parseInt(), whatever suits you):
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)
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);
\$(“Coefficient of Variation: ” + cov + ““).appendTo(‘#cvdisplay’);

The issue is the javascript line total=(total+field.value); which results in 0332334 instead of 18 as expected. String concatenation is being applied instead of numeric addition.
You can fix this by parsing the integer value: 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];

Here, I changed the code around a bit and got it to work. I basically isolated the segments a bit more. Made it more direct.
\$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);
?>

PHP Output:

Here’s a direct translation of the function you provided. You have to pass in a javascript array of numbers, and it produces the result you’re looking for (at least according to unit tests written in Node.js). You should to the type conversion (string-to-array) in another function to separate your concerns and make the code easier to reason about;
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;
};