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Implement Fisher Yates algorithm #172

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Merged
mchav merged 3 commits into from
Mar 2, 2026
Merged

Implement Fisher Yates algorithm #172

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7eaf4e7
Implement Fisher Yates algorithm
kayvank Mar 1, 2026
3e69bd5
Clean up build warnings
kayvank Mar 1, 2026
0b00734
Unit tests for Fisher Yates algorithm
kayvank Mar 2, 2026
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28 changes: 21 additions & 7 deletions src/DataFrame/Operations/Permutation.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,16 +9,17 @@
import qualified Data.Text as T
import qualified Data.Vector as V
import qualified Data.Vector.Unboxed as VU
import qualified Data.Vector.Unboxed.Mutable as VUM

import Control.Exception (throw)
import Control.Monad.ST (runST)
import DataFrame.Errors (DataFrameException (..))
import DataFrame.Internal.Column
import DataFrame.Internal.Column (Columnable, atIndicesStable)
import DataFrame.Internal.DataFrame (DataFrame (..))
import DataFrame.Internal.Expression
import DataFrame.Internal.Row
import DataFrame.Operations.Core
import System.Random
import System.Random.Shuffle (shuffle')
import DataFrame.Internal.Expression (Expr (Col))
import DataFrame.Internal.Row (sortedIndexes', toRowVector)
import DataFrame.Operations.Core (columnNames, dimensions)
import System.Random (Random (randomR), RandomGen)

-- | Sort order taken as a parameter by the 'sortBy' function.
data SortOrder where
Expand Down Expand Up @@ -76,4 +77,17 @@
df{columns = V.map (atIndicesStable indexes) (columns df)}

shuffledIndices :: (RandomGen g) => g -> Int -> VU.Vector Int
shuffledIndices pureGen k = VU.fromList (shuffle' [0 .. (k - 1)] k pureGen)
shuffledIndices pureGen k = shuffleVec pureGen (VU.fromList [0 .. (k - 1)])
where
shuffleVec :: (RandomGen g) => g -> VU.Vector Int -> VU.Vector Int
shuffleVec g v = runST $ do
vm <- VU.thaw v
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@mchav mchav Mar 1, 2026

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Instead of declaring the vector from list just to thaw it we can just create a new one in the shuffle vec function.

let (n, nGen) = randomR (0, (k - 1)) g

Check warning on line 85 in src/DataFrame/Operations/Permutation.hs

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GitHub Actions / hlint 

Suggestion in shuffledIndices in module DataFrame.Operations.Permutation: Redundant bracket ▫︎ Found: "(0, (k - 1))" ▫︎ Perhaps: "(0, k - 1)"
go vm n nGen
VU.unsafeFreeze vm

go v (-1) _ = pure ()
go v 0 _ = pure ()
go v maxInd gen =
let (n, nextGen) = randomR (0, maxInd) gen
in VUM.swap v 0 n *> go (VUM.tail v) (maxInd - 1) nextGen
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