Haskell find and replace values from list using map

Question

I have a list of lists in single chars like: [["a"],["b"],["c"],["d"]], and I have a map for example [("a", "A"), ("b", "B")], I would like to find elements in list that match the map keys and replace the list value with the map value for that key and remove all of the remaining unchanged single chars.

So for example from the above, if I have list of [["a"],["b"],["c"],["d"]] and map of [("a", "A"), ("b", "B")] I want to get back a single list like this: ["A", "B"]

As I am a total noob with Haskell so any help will be appreciated :)

Well thats simply how my input data is, but it can be transformed anyway to achieve the end goal — Monolith
– Monolith, Commented Nov 8, 2020 at 12:37
Does this answer your question? Haskell. INNER JOIN of two lists — Mark Seemann
– Mark Seemann, Commented Nov 8, 2020 at 12:42

Aplet123 · Accepted Answer · 2020-11-08 12:43:43Z

2

You can combine lookup with catMaybes:

import Data.Maybe

list :: [[String]]
list = [["a"],["b"],["c"],["d"]]

replacements :: [(String, String)]
replacements = [("a", "A"), ("b", "B")]

replaced :: [String]
replaced = catMaybes . map (\x -> lookup x replacements) . concat $ list

main :: IO ()
main = print replaced -- ["A", "B"]

answered Nov 8, 2020 at 12:43

Aplet123

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