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Implement Fisher Yates algorithm #172

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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
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1 change: 0 additions & 1 deletion dataframe.cabal
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Original file line number Diff line number Diff line change
Expand Up @@ -106,7 +106,6 @@ library
process ^>= 1.6,
snappy-hs ^>= 0.1,
random >= 1.2 && < 1.3,
random-shuffle >= 0.0.4 && < 1,
regex-tdfa >= 1.3.0 && < 2,
scientific >=0.3.1 && <0.4,
template-haskell >= 2.0 && < 3,
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30 changes: 23 additions & 7 deletions src/DataFrame/Operations/Permutation.hs
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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 +77,19 @@
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
| k <= 0 = VU.empty
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@kayvank kayvank Mar 2, 2026

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We return empty vector even when k is a negative number, which does not seen correct.
Should we error inf the rare event that k < 0? @mchav

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@mchav mchav Mar 2, 2026

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I think that's fine since the number is derived from the size of the dataframe. And the shuffle of an empty dataframe is an empty dataframe.

| otherwise = shuffleVec pureGen
where
shuffleVec :: (RandomGen g) => g -> VU.Vector Int
shuffleVec g = runST $ do
vm <- VUM.generate k id
let (n, nGen) = randomR (1, (k - 1)) g

Check warning on line 87 in src/DataFrame/Operations/Permutation.hs

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GitHub Actions / hlint 

Suggestion in shuffledIndices in module DataFrame.Operations.Permutation: Redundant bracket ▫︎ Found: "(1, (k - 1))" ▫︎ Perhaps: "(1, 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 (1, maxInd) gen
in VUM.swap v 0 n *> go (VUM.tail v) (maxInd - 1) nextGen