Read a comma-separated value (CSV) bytestream into a series.

Consider the following bytestream read from a file:

latitude,longitude,city
48.856667,2.352222,Paris
40.712778,-74.006111,New York City
25.0375,121.5625,Taipei
-34.603333,-58.381667,Buenos Aires

We want to get a series of the latitude an longitude, indexed by the column "city". First, we need to do is to create a datatype representing the latitude and longitude information, and our index:

import qualified Data.Vector.Unboxed         as U
import qualified Data.Vector.Unboxed.Mutable as UM
import qualified Data.Vector.Generic         as G
import qualified Data.Vector.Generic.Mutable as GM

newtype Latitude = MkLatitude Double
    deriving (Show)

-- Special code to ensure that Latitude is unboxed
-- This is only required for unboxed Series
newtype instance UM.MVector s Latitude = MV_Latitude (UM.MVector s Int)
newtype instance U.Vector Latitude = V_Latitude (U.Vector Int)
deriving instance GM.MVector UM.MVector Latitude
deriving instance G.Vector U.Vector Latitude 
instance U.Unbox Latitude

newtype City = MkCity String
    deriving ( Eq, Ord, Show )

Second, we need to create an instance of FromNamedRecord for our new types:

import Data.Csv ( FromNamedRecord, (.:) )

instance FromNamedRecord Latitude where
    parseNamedRecord r = MkLatitude <$> r .: "latitude"


instance FromNamedRecord City where
    parseNamedRecord r = MkCity <$> r .: "city"

Finally, we're ready to read our stream:

import Data.Series.Unboxed
import Data.Series.Unboxed.IO

main :: IO ()
main = do
    stream <- (...) -- Read the bytestring from somewhere
    let (latitudes  :: Series City Latitude) = either error id (readCSV stream)
    print latitudes

This is a helper function to read a CSV directly from a filepath. See the documentation for readCSV on how to prepare your types. Then, for example, you can use readCSVFromFile as:

import Data.Series.Unboxed
import Data.Series.Unboxed.IO

main :: IO ()
main = do
    let (latlongs  :: Series City LatLong) = either error id <$> readCSVFromFile "somefile.csv"
    print latitudes

Serialize a Series to bytes.

This is a helper function to write a Series directly to a file.