Build a sampleM for the monadic interface

Fixes #136

Author: amiri

src/DataFrame/Monad.hs

@@ -14,6 +14,7 @@ import DataFrame.Internal.Column (Columnable)
 import DataFrame.Internal.Expression (Expr (..))
 
 import qualified Data.Text as T
+import System.Random
 
 -- A re-implementation of the state monad.
 -- `mtl` might be too heavy a dependency just to get
@@ -61,6 +62,9 @@ renameM expr newName = deriveM newName expr
 filterWhereM :: Expr Bool -> FrameM ()
 filterWhereM p = modifyM (D.filterWhere p)
 
+sampleM :: (RandomGen g) => g -> Double -> FrameM ()
+sampleM pureGen p = modifyM (D.sample pureGen p)
+
 filterJustM :: (Columnable a) => Expr (Maybe a) -> FrameM (Expr a)
 filterJustM (Col name) = FrameM $ \df ->
     let df' = D.filterJust name df

src/DataFrame/Operations/Subset.hs

@@ -18,11 +18,23 @@ import qualified Prelude
 
 import Control.Exception (throw)
 import Data.Function ((&))
-import Data.Maybe (fromJust, fromMaybe, isJust, isNothing)
+import Data.Maybe (
+    fromJust,
+    fromMaybe,
+    isJust,
+    isNothing,
+ )
 import Data.Type.Equality (TestEquality (..))
-import DataFrame.Errors (DataFrameException (..), TypeErrorContext (..))
+import DataFrame.Errors (
+    DataFrameException (..),
+    TypeErrorContext (..),
+ )
 import DataFrame.Internal.Column
-import DataFrame.Internal.DataFrame (DataFrame (..), empty, getColumn)
+import DataFrame.Internal.DataFrame (
+    DataFrame (..),
+    empty,
+    getColumn,
+ )
 import DataFrame.Internal.Expression
 import DataFrame.Internal.Interpreter
 import DataFrame.Operations.Core