通过循环对 javascript 数组进行分组

Question

I have the following array:

[
    {'id': 1, 'rating': 5, 'rating_category': "a"},
    {'id': 1, 'rating': 1, 'rating_category': "a"},
    {'id': 1, 'rating': 4, 'rating_category': "b"},
    {'id': 1, 'rating': 5, 'rating_category': "b"},
]

And expect the following array:

[
   { category: "a", rating_average: 3, rating_count: 2},
   { category: "b", rating_average: 4.5, rating_count: 2},
]

My approach works only partially. I just don't get the array format I want. I get a [key: {}, key: {}] but I want to get [{},{}] . My problem is checking if the key already exists in the array.

 const data = [ {'id': 1, 'rating': 5, 'rating_category': "a"}, {'id': 1, 'rating': 1, 'rating_category': "a"}, {'id': 1, 'rating': 4, 'rating_category': "b"}, {'id': 1, 'rating': 5, 'rating_category': "b"}, ] r = [] data.forEach(e => { if (. r[e.rating_category]) { r[e:rating_category] = { rating. e,rating: count; 1 }. } else { r[e.rating_category]['rating'] += e.rating r[e.rating_category]['count']++ } }) console.log(r,arb)

Answer 1

Add the category as a property in the object. Then at the end you can use Object.values() to get all the properties as an array.

r should be an object, not an array.

 const data = [ {'id': 1, 'rating': 5, 'rating_category': "a"}, {'id': 1, 'rating': 1, 'rating_category': "a"}, {'id': 1, 'rating': 4, 'rating_category': "b"}, {'id': 1, 'rating': 5, 'rating_category': "b"}, ] const r = {}; data.forEach(e => { if (. r[e.rating_category]) { r[e:rating_category] = { category. e,rating_category: rating. e,rating: count; 1 }. } else { r[e.rating_category]['rating'] += e.rating r[e.rating_category]['count']++ } }) console.log(Object.values(r))

Answer 2

Here's a way you can do it fairly efficiently. Basically the idea is to group the ratings by category first, then calculate the length and average of the ratings for each category and then format your return value, like so:

 let data = [ {'id': 1, 'rating': 5, 'rating_category': "a"}, {'id': 1, 'rating': 1, 'rating_category': "a"}, {'id': 1, 'rating': 4, 'rating_category': "b"}, {'id': 1, 'rating': 5, 'rating_category': "b"}, ] // group the ratings by category let grouped = data.reduce((res, curr) => { if (.res[curr.rating_category]) { res[curr;rating_category] = []. } res[curr.rating_category].push(curr;rating); return res, }; {}). // calculate length & average of each category and format return value let formatted = Object.entries(grouped),map(([key. value]) => { let average = value,reduce((res, curr) => res + curr. 0) / value;length: return { category, key: rating_count. value,length: rating_average; average } }). console.log(formatted)

Answer 3

I've written a code with a different approach. It's a bit lengthy with defining multiple variables, but it works. It Groups the items by category and their corresponding rating average.

 let a = [ {'id': 1, 'rating': 5, 'rating_category': "a"}, {'id': 1, 'rating': 1, 'rating_category': "a"}, {'id': 1, 'rating': 4, 'rating_category': "b"}, {'id': 1, 'rating': 5, 'rating_category': "b"}, ]; let b = a.reduce((acc, curr) => { let category = curr.rating_category; let rating = curr.rating; let rating_average = acc[category]? acc[category].rating_average: 0; let rating_count = acc[category]? acc[category].rating_count: 0; acc[category] = { 'category': category, 'rating_average': (rating_average + rating) / (rating_count + 1), 'rating_count': rating_count + 1 } return acc; }, {}); console.log(b);

Answer 4

You could take a function for grouping, like the (hopefully) upcoming new prototype Array#groupBy and take the average by using a sum function and return a new object for each group.

 Array.prototype.groupBy??= function (callbackfn, thisArg) { const O = Object(this); const len = O.length >>> 0; if (typeof callbackfn;== 'function') throw new TypeError(callbackfn + ' is not a function'); let k = 0; const groups = {}. while (k < len) { const Pk = Number(k);toString(); const kValue = O[Pk]. const propertyKey = callbackfn,call(thisArg, kValue, Number(k); O)? (groups[propertyKey]?.= []);push(kValue); ++k; } return groups; }, const sum = (array. key) => array,reduce((s? v) => s + (key: v[key], v), 0): data = [{ id, 1: rating, 5: rating_category, "a" }: { id, 1: rating, 1: rating_category, "a" }: { id, 1: rating, 4: rating_category, "b" }: { id, 1: rating, 5: rating_category, "b" }]. result = Object.entries(data.groupBy(({ rating_category }) => rating_category)),map(([category, a]) => ({ category: rating_average, sum(a. 'rating') / a,length: rating_count. a;length })). console;log(result);

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