From 5bc71959492b2379e5b80eaf367352d3a09ff220 Mon Sep 17 00:00:00 2001
From: skymanbp <57272723+skymanbp@users.noreply.github.com>
Date: Fri, 25 Sep 2026 01:14:17 -0400
Subject: [PATCH] fix: keep nulls in nullable int32 and int64 decimal parquet
 columns

---
 dataframe-parquet/src/DataFrame/IO/Parquet.hs |  16 ++++++----------
 tests/Parquet.hs                              |  14 ++++++++++++++
 tests/data/nullable_int_decimal.parquet       | Bin 0 -> 812 bytes
 3 files changed, 20 insertions(+), 10 deletions(-)
 create mode 100644 tests/data/nullable_int_decimal.parquet

diff --git a/dataframe-parquet/src/DataFrame/IO/Parquet.hs b/dataframe-parquet/src/DataFrame/IO/Parquet.hs
index bbfb774d..71f1d8cf 100644
--- a/dataframe-parquet/src/DataFrame/IO/Parquet.hs
+++ b/dataframe-parquet/src/DataFrame/IO/Parquet.hs
@@ -674,18 +674,14 @@ applyLogicalType (Just (LT_DECIMAL f)) col =
         scale = unField dt.decimal_scale
         precision = unField dt.decimal_precision
      in if precision <= 9
-            then case DI.toVector @Int32 @VU.Vector col of
-                Right xs ->
-                    DI.fromUnboxedVector $
-                        VU.map (\raw -> fromIntegral @Int32 @Double raw / 10 ^ scale) xs
-                Left _ -> col
+            then
+                fromRight col $
+                    DI.mapColumn (\raw -> fromIntegral @Int32 @Double raw / 10 ^ scale) col
             else
                 if precision <= 18
-                    then case DI.toVector @Int64 @VU.Vector col of
-                        Right xs ->
-                            DI.fromUnboxedVector $
-                                VU.map (\raw -> fromIntegral @Int64 @Double raw / 10 ^ scale) xs
-                        Left _ -> col
+                    then
+                        fromRight col $
+                            DI.mapColumn (\raw -> fromIntegral @Int64 @Double raw / 10 ^ scale) col
                     else col
 applyLogicalType _ col = col
 
diff --git a/tests/Parquet.hs b/tests/Parquet.hs
index 5e48e136..dcb2dd30 100644
--- a/tests/Parquet.hs
+++ b/tests/Parquet.hs
@@ -823,6 +823,19 @@ int64Decimal =
             )
         )
 
+nullableIntDecimal :: Test
+nullableIntDecimal = testBothReadParquetPaths $ \readParquet ->
+    TestCase
+        ( assertEqual
+            "nullableIntDecimal"
+            ( D.fromNamedColumns
+                [ ("int32_dec", D.fromList [Just (1 :: Double), Nothing, Just 2.5, Just 0.75])
+                , ("int64_dec", D.fromList [Nothing, Just (1234.5 :: Double), Nothing, Just (-5)])
+                ]
+            )
+            (unsafePerformIO (readParquet "./tests/data/nullable_int_decimal.parquet"))
+        )
+
 byteArrayDecimal :: Test
 byteArrayDecimal =
     TestCase
@@ -1394,6 +1407,7 @@ tests =
     , -- Group 7: decimal types
       int32Decimal
     , int64Decimal
+    , nullableIntDecimal
     , byteArrayDecimal
     , fixedLengthDecimal
     , fixedLengthDecimalLegacy
diff --git a/tests/data/nullable_int_decimal.parquet b/tests/data/nullable_int_decimal.parquet
new file mode 100644
index 0000000000000000000000000000000000000000..a3daa296ce642a034c1cbedcb63f96881fed9f54
GIT binary patch
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