Move getColumn out of DataSet

It doesn't really belong there - currently the DataSet is just the
interface to feed data to LightGBM.  Nothing more.

examples/titanic/Main.hs

@@ -1,6 +1,7 @@
 -- | Titanic survivorship example
 
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE RecordWildCards #-}
 {-# LANGUAGE TemplateHaskell #-}
 
 module Main where
@@ -52,6 +53,14 @@ accuracy predictions knowns =
       totalCount = length matches
    in fromIntegral matchCount / fromIntegral totalCount
 
+-- | Convert a DataSet into a list of records for whatever type is relevant.
+getColumn :: Read a => Int -> DS.DataSet -> IO [a]
+getColumn colIndex DS.CSVFile {..} =
+  V.toList . readColumn colIndex (conv hasHeader) <$> BSL.readFile dataPath
+  where
+    conv (DS.HasHeader True) = CSV.HasHeader
+    conv (DS.HasHeader False) = CSV.NoHeader
+
 trainModel :: IO LGBM.Model
 trainModel =
   TMP.withSystemTempFile "filtered_train" $ \trainFile trainHandle -> do
@@ -75,7 +84,7 @@ trainModel =
           case predResults of
             Left e -> error $ "Error preticting results:  " ++ show e
             Right predictionSet -> do
-              predictions <- DS.getColumn 0 predictionSet :: IO [Double]
+              predictions <- getColumn 0 predictionSet :: IO [Double]
               LGBM.writeCsvFile predictionFile predictionSet
 
               valData <- BSL.readFile valFile

src/LightGBM/DataSet.hs

@@ -5,16 +5,10 @@ module LightGBM.DataSet (
     DataSet (..)
   , HasHeader(..)
   , readCsvFile
-  , writeCsvFile
-  , getColumn) where
+  , writeCsvFile) where
 
-import qualified Data.ByteString.Lazy as BSL
-import qualified Data.Csv as CSV
-import qualified Data.Vector as V
 import           System.Directory (copyFile)
 
-import           LightGBM.Utils.Csv (readColumn)
-
 -- N.B.  Right now it's just a data file, but we can add better types
 -- (e.g. some sort of dataframe) as other options as we move forward.
 -- | A set of data to use for training or prediction.
@@ -51,11 +45,3 @@ writeCsvFile ::
   -> DataSet -- ^ The data to persist
   -> IO ()
 writeCsvFile outPath CSVFile {..} = copyFile dataPath outPath
-
--- | Convert a DataSet into a list of records for whatever type is relevant.
-getColumn :: Read a => Int -> DataSet -> IO [a]
-getColumn colIndex CSVFile {..} =
-  V.toList . readColumn colIndex (conv hasHeader) <$> BSL.readFile dataPath
-  where
-    conv (HasHeader True) = CSV.HasHeader
-    conv (HasHeader False) = CSV.NoHeader