Haskell | How to convert list of numbers in CSV file to a list containing lists-CodePudding

Not particularly great with Haskell here. Just getting started with I/O with Haskell

I have a CSV file with a single column with numbers as follows:

I have a function that takes in the name of the file and prints out a single list containing lists for each line of the CSV of type:

    printList :: String -> IO ()
    printList nameOfinputFile = do
                                s <- readFile inp
                                ..................
                                ..................
                                ..................
                                print (splitList)

where splitList is the intended output and for the given CSV file example, and it's meant to look like:

[ [1,2,3],[4,5],[6,7,8,9],[10],[11,12,13,14,15],[16],[17] ]

How can I implement this while preserving the type of my function?

CodePudding user response：

This works on Replit:

import Data.List(lines)
import Distribution.Simple.Utils(unintersperse)

splitList :: String -> [[Int]]
splitList = map (map read . unintersperse ',') . lines

CodePudding user response：

There are likely to be many ways of doing the same thing. This is my version:

import Data.List.Split

convList [] = []
convList [""] = []
convList xs = map (\x -> read x :: Int) xs

main = do
    content <- readFile "Test.csv"
    let valuesStr = map (splitOn ",") $ lines content
    let valuesInt = map convList valuesStr

    print valuesInt

The main function uses readFile to slurp in the CSV file. The function lines is used to split the content, and then splitOn is mapped over the lines. Finally, a new function convList is mapped over the values inside each list. The function convList has three possibilities:

Empty list, yields an empty list
Blank line, yields an empty list
Elements exist, yields values (here Int, could be Double)

Result with extra blank line:

[[1,2,3],[4,5],[6,7,8,9],[10],[11,12,13,14,15],[16],[17],[]]