Shuffle.hs

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TypeApplications #-}

module Operations.Shuffle where

import qualified DataFrame as D

import DataFrame.Operations.Permutation (shuffle)
import System.Random (mkStdGen)
import Test.HUnit (Test (..), assertEqual)

testDataFrame :: D.DataFrame
testDataFrame =
    D.fromNamedColumns
        [ ("numbers", D.fromList @Int [1 .. 26])
        ]

-- Test that shuffling does anything at all
shuffleShuffles :: Test
shuffleShuffles =
    let gen = mkStdGen 1234
        shuffled = shuffle gen testDataFrame
        initialNumbers = D.extractNumericColumn "numbers" testDataFrame
        shuffledNumbers = D.extractNumericColumn "numbers" shuffled
     in TestCase
            ( assertEqual
                "Shuffled column unequal to initial column"
                False
                (initialNumbers == shuffledNumbers)
            )

shufflePreservesColumnNames :: Test
shufflePreservesColumnNames =
    let gen = mkStdGen 837
        shuffled = shuffle gen testDataFrame
     in TestCase
            ( assertEqual
                "Column names are unchanged"
                (D.columnNames shuffled)
                (D.columnNames testDataFrame)
            )

-- Test that un-shuffling restores the original dataframe
-- which is known to be sorted in this case
shufflePreservesData :: Test
shufflePreservesData =
    let gen = mkStdGen 1234
        shuffled = shuffle gen testDataFrame
        sortedShuffled = D.sortBy [D.Asc (D.col @Int "numbers")] shuffled
     in TestCase
            (assertEqual "sort recovers initial numbers" testDataFrame sortedShuffled)

-- Test that shuffling isn't doing anything sneaky with summoning
-- random numbers somehow
shuffleSameSeedIsSameShuffle :: Test
shuffleSameSeedIsSameShuffle =
    let gen = mkStdGen 1234
        shuffled1 = shuffle gen testDataFrame
        shuffled2 = shuffle gen testDataFrame
     in TestCase
            (assertEqual "shuffle with same seed gives same result" shuffled1 shuffled2)

-- Test that different seeds give different results
shuffleDifferentSeedIsDifferent :: Test
shuffleDifferentSeedIsDifferent =
    let gen1 = mkStdGen 1234
        gen2 = mkStdGen 4321
        shuffled1 = shuffle gen1 testDataFrame
        shuffled2 = shuffle gen2 testDataFrame
     in TestCase
            ( assertEqual
                "shuffle with different seeds gives different results"
                False
                (shuffled1 == shuffled2)
            )

tests :: [Test]
tests =
    [ TestLabel "shuffleShuffles" shuffleShuffles
    , TestLabel "shufflePreservesData" shufflePreservesData
    , TestLabel "shufflePreservesColumnNames" shufflePreservesColumnNames
    , TestLabel "shuffleSameSeedIsSameShuffle" shuffleSameSeedIsSameShuffle
    , TestLabel "shuffleDifferentSeedIsDifferent" shuffleDifferentSeedIsDifferent
    ]