CODEWITHSUNDEEP
haskellfilteraverage
josvankamp
josvankamp

Reputation: 49

Calculate average from a list of data

I have a list reviews and that list is filled with:

    data Review = Review artist::String score::Integer Tour String String Locatie [String]

So what I'm trying to do is to calculate the average score of the reviews from a specific artist. What I have so far is a function to filter also the reviews of a artist like so:

    filterByArtiest :: String -> [Review] -> [Review]
    filterByArtiest art = filter (\a -> artiest a == art)

And this is what I had in mind to calculate the average:

    gem :: String -> (String -> [Review] -> [Review]) -> Double
    gem art =

But I have like no idea how to finish that function to calculate the average.

Upvotes: 2

Views: 1082

Answers (2)

mhwombat
mhwombat

Reputation: 8136

First, you need to filter your list to get just the reviews for a partticular artist. If your list of reviews is called reviews, then something like this should work:

joesReviews = filter (\review -> artist review == "Joe Bloggs") reviews

Next, extract all of the scores into a list.

scores = map score joesReviews

Now you can use sum scores to determine the total score. Then use length scores to calculate the number of values. Now you have everything you need to calculate the average.

Upvotes: 1

Sibi
Sibi

Reputation: 48664

What you have to do is simple:

  • Filter out that particular artist that you are interested at.
  • Extract (map) all the score of that particular artist.
  • Calculate his average by the list of scores obtained for that artist.

Assuming that your Review record is something like this:

data Review = Review {
     artist::String,
     score::Integer,
     tour :: String ,
     locatie :: [String] 
    }

You can calculate the average using this function:

average :: String -> [Review] -> Double
average artistName reviews = fromIntegral (sum scores) / fromIntegral (length scores)
    where artists = filterByArtiest artistName reviews
          scores = map score artists

Upvotes: 2

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