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fix: pow and daysBetween are not commutative #232

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Merged
mchav merged 1 commit into from
Sep 25, 2026
Merged

fix: pow and daysBetween are not commutative #232

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4 changes: 2 additions & 2 deletions dataframe-operations/src/DataFrame/Functions.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -460,7 +460,7 @@ zScore :: Expr Double -> Expr Double
zScore c = (c - mean c) / stddev c

pow :: (Columnable a, Num a) => Expr a -> Int -> Expr a
pow expr i = lift2Decorated (^) "pow" (Just "^") True 8 expr (Lit i)
pow expr i = lift2Decorated (^) "pow" (Just "^") False 8 expr (Lit i)
{-# SPECIALIZE pow :: Expr Double -> Int -> Expr Double #-}
{-# SPECIALIZE pow :: Expr Float -> Int -> Expr Float #-}
{-# SPECIALIZE pow :: Expr Int -> Int -> Expr Int #-}
Expand Down Expand Up @@ -645,7 +645,7 @@ daysBetween =
(\d1 d2 -> fromIntegral (diffDays d1 d2))
"daysBetween"
Nothing
True
False
2

bind ::
Expand Down
2 changes: 1 addition & 1 deletion docs/base/haskell_for_data_analysis.md
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Expand Up @@ -661,7 +661,7 @@ TIO.putStrLn $ D.toMarkdown withDates

```haskell
-- This requires two Day columns; here we illustrate the pattern:
-- D.derive "days_until" (F.daysBetween today_col deadline_col) df
-- D.derive "days_until" (F.daysBetween deadline_col today_col) df
```

### Opting into stronger type safety
Expand Down
2 changes: 1 addition & 1 deletion docs/haskell_for_data_analysis.md
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Expand Up @@ -1039,7 +1039,7 @@ TIO.putStrLn $ D.toMarkdown withDates

```haskell
-- This requires two Day columns; here we illustrate the pattern:
-- D.derive "days_until" (F.daysBetween today_col deadline_col) df
-- D.derive "days_until" (F.daysBetween deadline_col today_col) df
```


Expand Down
33 changes: 33 additions & 0 deletions tests/Functions.hs
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Expand Up @@ -3,6 +3,7 @@

module Functions where

import Data.Time.Calendar (Day, fromGregorian)
import qualified DataFrame as D
import DataFrame.Functions (
sanitize,
Expand Down Expand Up @@ -79,8 +80,40 @@ testSum =
(D.derive "sum" (F.sum (F.col @Int "A")) df)
)

testPow :: Test
testPow =
TestCase
( assertEqual
"pow of a compound base"
[4, 9, 16, 25, 36, 49, 64, 81, 100, 121]
( D.columnAsList @Int
(F.col "sq")
(D.derive "sq" (F.pow (F.col @Int "A" + F.lit 1) 2) df)
)
)

testDaysBetween :: Test
testDaysBetween =
TestCase
( assertEqual
"daysBetween d1 d2 is d1 minus d2 in either argument order"
([-9], [9])
( days (F.col @Day "start") (F.col @Day "end")
, days (F.col @Day "end") (F.col @Day "start")
)
)
where
dates =
D.fromNamedColumns
[ ("start", DI.fromList [fromGregorian 2024 3 1])
, ("end", DI.fromList [fromGregorian 2024 3 10])
]
days a b = D.columnAsList @Int (F.col "d") (D.derive "d" (F.daysBetween a b) dates)

tests :: [Test]
tests =
[ TestLabel "sanitizeIdentifiers" sanitizeIdentifiers
, TestLabel "testSum" testSum
, TestLabel "testPow" testPow
, TestLabel "testDaysBetween" testDaysBetween
]
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