替换当前值后求平均值 [英] Finding an average after replacing a current value

问题描述

不确定为什么会出现此问题，但是由于某种原因，我得到了错误的输出.我想做的是获取现有的平均收视率并生成新的收视率.我目前正在解决的情况是，已经计算出平均值的用户需要更改其值.

Not sure why this problem is occurring, but for some reason I'm getting the wrong output. What I'm trying to do is take an existing average of ratings and generate a new one. The case I'm currently solving is when a user who has already been calculated in the average needs their value changed.

例如:

User A rates at 5 stars
User B rates at 3 stars
User C rates at 5 star

当前平均星数是:13/3或4.333

Current average stars is: 13/3 or 4.333

现在，如果用户B更改了评分，并且我不想浏览所有评分，我只想说:

Now if user B changes their rating, and I don't want to go cycling through all ratings, I want to just say:

鉴于我知道有3个等级，而我要更改的等级是用户C到3，那么我想我可以做到:

Given that I know there are 3 ratings and the one I'm changing is user C to 3, then I would presume I can do:

13-5 = 8
8 + 3 = 11
11/3 = new average 3.667

var originalRatingVal = originalRating.rating ? originalRating.rating.stars : 0
var currentNumberOfRatings = currentItem.count ? currentItem.count.ratings : 0

var currentAverageTotal = currentNumberOfRatings * overall_rating
var oldNumberOfRatings = currentNumberOfRatings - 1
var newAverage = (currentAverageTotal - originalRatingVal) - oldNumberOfRatings

var newRatingVal = currentRating.rating ? currentRating.rating.stars : 0
var newNumRatings = oldNumberOfRatings + 1;
var oldRatingTotal = newAverage * oldNumberOfRatings;
var newAvgRating = (oldRatingTotal + newRatingVal) / newNumRatings;

这似乎不起作用:

如果我将用户B更改为5，期望newAvgRating等于5，则当前等于5.666666666666667.

If I change user B to 5, expecting newAvgRating to equal 5, it currently equals 5.666666666666667.

任何想法都将不胜感激，谢谢！

Any ideas would be extremely appreciated, thank you!

推荐答案

const ratings = [5, 3, 5];
const ratingsTotalled = ratings.reduce((a,b)=>a+b);
const originalAverage = ratingsTotalled/ratings.length;
console.log('original:', originalAverage);

//now, I want to remove a '5' rating
//and replace it with '3'

const alteredTotal = ratingsTotalled - 5 + 3;
const alteredAverage = alteredTotal/ratings.length;

console.log('altered:', alteredAverage);

换句话说:

const originalRatings = {
  a: 5,
  b: 3,
  c: 5,
}
const ratings = Object.values(originalRatings);
const ratingsTotalled = ratings.reduce((a,b)=>a+b);
const originalAverage = ratingsTotalled/ratings.length;
console.log('original:', originalAverage);

//now, I want to remove a '5' rating
//and replace it with '3'
const cAlteredRating = 3;
const alteredTotal = ratingsTotalled - originalRatings.c + cAlteredRating;
const alteredAverage = alteredTotal/ratings.length;

console.log('altered:', alteredAverage);

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