CODEWITHSUNDEEP
listsortinghaskell
Phroggyy
Phroggyy

Reputation: 433

Sort tuples within list in Haskell

So, having scoured the Internet for quite some time for a nice solution, I have arrived at the end of the road.

I am currently faced with a few Haskell problems regarding text-handling, and most of it has been going perfectly fine. However, I am now stuck at sorting tuples within a list.

Basically, I have a list of tuples, so something along the lines of

list = [("hey","there"),("there","hey"),("bears","are")]

My goal now is to sort the tuples internally so that I receive

list = [("hey","there"),("hey","there"),("are","bears")]

Which I will then run a group $ sort list on to be able to retrieve a tally of how many equivalent pairs there are. In other words, ("hey,"there")is equivalent to ("there","hey").

What I have tried so far is using a map function. However, it seems that you cannot run list operations using the map function, but to at least attempt to understand what my final goal is, here is what I have achieved so far.

countup tuples =
    let final =
        sort sorted_internal where
            sorted_internal = map (\x->(sort x)) tuples
    in map (\x->(head x, length x)) final

Upvotes: 0

Views: 616

Answers (1)

MathematicalOrchid
MathematicalOrchid

Reputation: 62818

The sort function can't sort the elements of a tuple; it only works for lists.

You have two options. One is to write a function for sorting (2-element) tuples:

sortTuple :: (Ord a) => (a,a) -> (a,a)
sortTuple (x,y) = (min x y, max x y)

map sortTuple tuples

The other is to use lists instead of tuples:

map sort [["hey","there"], ["hey","there"], ["are","bears"]]

Upvotes: 10

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