CODEWITHSUNDEEP
javascriptrating-system
randomz
randomz

Reputation: 1

Javascript - Calculate missing 5 stars to reach desired rating

I would like to make a script that calculate how many "5" I need to reach 4.95 rating.

I created an object:

var obMed = {
   5: 0,
   4: 0,
   3: 0,
   2: 0,
   1: 0
 };

I got this function to update previous object with my rating

function upOB(a,b,c,d,e) {
    obMed["5"] = a;
    obMed["4"] = b;
    obMed["3"] = c;
    obMed["2"] = d;
    obMed["1"] = e;
    return obMed;
}

And this function to get the rating value

function med(obj) {
    div = obj["5"] + obj["4"] + obj["3"] + obj["2"] + obj["1"];
    somma = (obj["5"] * 5) + (obj["4"] * 4) + (obj["3"] * 3) + (obj["2"] * 2) + (obj["1"] * 1);
    media = (somma/div).toFixed(2);
    return media;
}

At this point I would like to add 1 to object["5"] until my average is greater than or equal to 4.95 but I'm really stuck.

I tried loops with no results, probably I wrote them bad.

Upvotes: 0

Views: 131

Answers (2)

Daniel Reina
Daniel Reina

Reputation: 6327

If you do the equations you get the following relation (using the same variable names that your code uses)

function getNeed(div, somma) {
  return Math.ceil((4.95*div - somma) / 0.05);
}

As I understand that div is the total amount of votes sent, and somma is the sum of all scores.


Math behind the method

current score: somma / div
if you add N votes of 5 stars, the new score would be: (somma + N * 5) / (div + N)
If you want that to be equal to 4.95, then you do (somma + N * 5) / (div + N) = 4.95, and the result is that:
N = (4.95*div - somma) / 0.05

Then you'll have to ceil that value as @dvsoukup commented, as you cannot have a non-integer amount of votes. This way, for example, you would have as a result 7 if the value of the computed N was 6.72.

Upvotes: 1

Christian Vincenzo Traina
Christian Vincenzo Traina

Reputation: 10374

It's a math problem. You calculate your average in this way:

( k1*1 + k2*2 + k3*3 + k4*4 + k5*5 ) / (k1 + k2 + k3 + k4 + k5)

Where k1..5 is the number of votes. You want to know the number j of votes to reach 4.95.

Your position is:

( k1*1 + k2*2 + k3*3 + k4*4 + (k5+j)*5 ) / (k1 + k2 + k3 + k4 + k5+j) = 4.95

With some math passage, that I save you, your result is:

j = 79*k1 + 59*k2 + 39*k3 + 19*k4 - k5

Apply this formula and you will get your desired number

Coming back with javascript, you have to consider:

var missingFives = 79*obMed[1]+59*obMed[2]+39*obMed[3]+19*obMed[4]-obMed[5];

Upvotes: 0

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