Optimized slicing

src/array/binary/mod.rs

@@ -203,7 +203,8 @@ impl<O: Offset> BinaryArray<O> {
         let validity = self
             .validity
             .clone()
-            .map(|x| x.slice_unchecked(offset, length));
+            .map(|bitmap| bitmap.slice_unchecked(offset, length))
+            .and_then(|bitmap| (bitmap.unset_bits() > 0).then(|| bitmap));
         let offsets = self.offsets.clone().slice_unchecked(offset, length + 1);
         Self {
             data_type: self.data_type.clone(),

src/array/boolean/mod.rs

@@ -167,7 +167,8 @@ impl BooleanArray {
         let validity = self
             .validity
             .clone()
-            .map(|x| x.slice_unchecked(offset, length));
+            .map(|bitmap| bitmap.slice_unchecked(offset, length))
+            .and_then(|bitmap| (bitmap.unset_bits() > 0).then(|| bitmap));
         Self {
             data_type: self.data_type.clone(),
             values: self.values.clone().slice_unchecked(offset, length),

src/array/fixed_size_binary/mod.rs

@@ -131,7 +131,8 @@ impl FixedSizeBinaryArray {
         let validity = self
             .validity
             .clone()
-            .map(|x| x.slice_unchecked(offset, length));
+            .map(|bitmap| bitmap.slice_unchecked(offset, length))
+            .and_then(|bitmap| (bitmap.unset_bits() > 0).then(|| bitmap));
         let values = self
             .values
             .clone()

src/array/fixed_size_list/mod.rs

@@ -150,7 +150,8 @@ impl FixedSizeListArray {
         let validity = self
             .validity
             .clone()
-            .map(|x| x.slice_unchecked(offset, length));
+            .map(|bitmap| bitmap.slice_unchecked(offset, length))
+            .and_then(|bitmap| (bitmap.unset_bits() > 0).then(|| bitmap));
         let values = self
             .values
             .clone()

src/array/list/mod.rs

@@ -222,7 +222,8 @@ impl<O: Offset> ListArray<O> {
         let validity = self
             .validity
             .clone()
-            .map(|x| x.slice_unchecked(offset, length));
+            .map(|bitmap| bitmap.slice_unchecked(offset, length))
+            .and_then(|bitmap| (bitmap.unset_bits() > 0).then(|| bitmap));
         let offsets = self.offsets.clone().slice_unchecked(offset, length + 1);
         Self {
             data_type: self.data_type.clone(),

src/array/map/mod.rs

@@ -167,7 +167,8 @@ impl MapArray {
         let validity = self
             .validity
             .clone()
-            .map(|x| x.slice_unchecked(offset, length));
+            .map(|bitmap| bitmap.slice_unchecked(offset, length))
+            .and_then(|bitmap| (bitmap.unset_bits() > 0).then(|| bitmap));
         Self {
             data_type: self.data_type.clone(),
             offsets,

src/array/primitive/mod.rs

@@ -233,7 +233,8 @@ impl<T: NativeType> PrimitiveArray<T> {
         let validity = self
             .validity
             .clone()
-            .map(|x| x.slice_unchecked(offset, length));
+            .map(|bitmap| bitmap.slice_unchecked(offset, length))
+            .and_then(|bitmap| (bitmap.unset_bits() > 0).then(|| bitmap));
         Self {
             data_type: self.data_type.clone(),
             values: self.values.clone().slice_unchecked(offset, length),

src/array/struct_/mod.rs

@@ -198,7 +198,8 @@ impl StructArray {
         let validity = self
             .validity
             .clone()
-            .map(|x| x.slice_unchecked(offset, length));
+            .map(|bitmap| bitmap.slice_unchecked(offset, length))
+            .and_then(|bitmap| (bitmap.unset_bits() > 0).then(|| bitmap));
         Self {
             data_type: self.data_type.clone(),
             values: self

src/array/utf8/mod.rs

@@ -220,7 +220,8 @@ impl<O: Offset> Utf8Array<O> {
         let validity = self
             .validity
             .clone()
-            .map(|x| x.slice_unchecked(offset, length));
+            .map(|bitmap| bitmap.slice_unchecked(offset, length))
+            .and_then(|bitmap| (bitmap.unset_bits() > 0).then(|| bitmap));
         // + 1: `length == 0` implies that we take the first offset.
         let offsets = self.offsets.clone().slice_unchecked(offset, length + 1);
         Self {