alamb commented on code in PR #4579:
URL: https://github.com/apache/arrow-rs/pull/4579#discussion_r1277727180


##########
arrow-select/src/take.rs:
##########
@@ -331,94 +331,68 @@ fn take_bytes<T: ByteArrayType, IndexType: 
ArrowPrimitiveType>(
     let data_len = indices.len();
 
     let bytes_offset = (data_len + 1) * std::mem::size_of::<T::Offset>();
-    let mut offsets_buffer = MutableBuffer::from_len_zeroed(bytes_offset);
+    let mut offsets = MutableBuffer::new(bytes_offset);
+    offsets.push(T::Offset::default());
 
-    let offsets = offsets_buffer.typed_data_mut();
     let mut values = MutableBuffer::new(0);
-    let mut length_so_far = T::Offset::from_usize(0).unwrap();
-    offsets[0] = length_so_far;
 
     let nulls;
     if array.null_count() == 0 && indices.null_count() == 0 {
-        for (i, offset) in offsets.iter_mut().skip(1).enumerate() {
-            let index = indices.value(i).to_usize().ok_or_else(|| {
-                ArrowError::ComputeError("Cast to usize failed".to_string())
-            })?;
-
-            let s = array.value(index);
-
-            let s: &[u8] = s.as_ref();
-            length_so_far += T::Offset::from_usize(s.len()).unwrap();
+        offsets.extend(indices.values().iter().map(|index| {
+            let s: &[u8] = array.value(index.as_usize()).as_ref();
             values.extend_from_slice(s);
-            *offset = length_so_far;
-        }
+            T::Offset::usize_as(values.len())
+        }));
         nulls = None
     } else if indices.null_count() == 0 {
         let num_bytes = bit_util::ceil(data_len, 8);
 
         let mut null_buf = 
MutableBuffer::new(num_bytes).with_bitset(num_bytes, true);
         let null_slice = null_buf.as_slice_mut();
-
-        for (i, offset) in offsets.iter_mut().skip(1).enumerate() {
-            let index = indices.value(i).to_usize().ok_or_else(|| {
-                ArrowError::ComputeError("Cast to usize failed".to_string())
-            })?;
-
+        offsets.extend(indices.values().iter().enumerate().map(|(i, index)| {
+            let index = index.as_usize();
             if array.is_valid(index) {
                 let s: &[u8] = array.value(index).as_ref();
-
-                length_so_far += T::Offset::from_usize(s.len()).unwrap();
                 values.extend_from_slice(s.as_ref());
             } else {
                 bit_util::unset_bit(null_slice, i);
             }
-            *offset = length_so_far;
-        }
+            T::Offset::usize_as(values.len())
+        }));
         nulls = Some(null_buf.into());
     } else if array.null_count() == 0 {
-        for (i, offset) in offsets.iter_mut().skip(1).enumerate() {
+        offsets.extend(indices.values().iter().enumerate().map(|(i, index)| {
             if indices.is_valid(i) {

Review Comment:
   ```suggestion
               // check index is valid before using index. The value in
               // NULL index slots may not be within bounds of array
               if indices.is_valid(i) {
   ```



##########
arrow-select/src/take.rs:
##########
@@ -1949,4 +1923,16 @@ mod tests {
             .collect::<Vec<_>>();
         assert_eq!(&values, &[Some(23), Some(4), None, None])
     }
+
+    #[test]
+    fn test_take_bytes_null_indices() {
+        let indices = Int32Array::new(

Review Comment:
   ```suggestion
           // Build indices with values that out of bounds, but NULL so they 
           // will not be checked
           let indices = Int32Array::new(
   ```



##########
arrow-select/src/take.rs:
##########
@@ -331,94 +331,68 @@ fn take_bytes<T: ByteArrayType, IndexType: 
ArrowPrimitiveType>(
     let data_len = indices.len();
 
     let bytes_offset = (data_len + 1) * std::mem::size_of::<T::Offset>();
-    let mut offsets_buffer = MutableBuffer::from_len_zeroed(bytes_offset);
+    let mut offsets = MutableBuffer::new(bytes_offset);
+    offsets.push(T::Offset::default());
 
-    let offsets = offsets_buffer.typed_data_mut();
     let mut values = MutableBuffer::new(0);
-    let mut length_so_far = T::Offset::from_usize(0).unwrap();
-    offsets[0] = length_so_far;
 
     let nulls;
     if array.null_count() == 0 && indices.null_count() == 0 {
-        for (i, offset) in offsets.iter_mut().skip(1).enumerate() {
-            let index = indices.value(i).to_usize().ok_or_else(|| {
-                ArrowError::ComputeError("Cast to usize failed".to_string())
-            })?;
-
-            let s = array.value(index);
-
-            let s: &[u8] = s.as_ref();
-            length_so_far += T::Offset::from_usize(s.len()).unwrap();
+        offsets.extend(indices.values().iter().map(|index| {
+            let s: &[u8] = array.value(index.as_usize()).as_ref();
             values.extend_from_slice(s);
-            *offset = length_so_far;
-        }
+            T::Offset::usize_as(values.len())
+        }));
         nulls = None
     } else if indices.null_count() == 0 {
         let num_bytes = bit_util::ceil(data_len, 8);
 
         let mut null_buf = 
MutableBuffer::new(num_bytes).with_bitset(num_bytes, true);
         let null_slice = null_buf.as_slice_mut();
-
-        for (i, offset) in offsets.iter_mut().skip(1).enumerate() {
-            let index = indices.value(i).to_usize().ok_or_else(|| {
-                ArrowError::ComputeError("Cast to usize failed".to_string())
-            })?;
-
+        offsets.extend(indices.values().iter().enumerate().map(|(i, index)| {
+            let index = index.as_usize();
             if array.is_valid(index) {
                 let s: &[u8] = array.value(index).as_ref();
-
-                length_so_far += T::Offset::from_usize(s.len()).unwrap();
                 values.extend_from_slice(s.as_ref());
             } else {
                 bit_util::unset_bit(null_slice, i);
             }
-            *offset = length_so_far;
-        }
+            T::Offset::usize_as(values.len())
+        }));
         nulls = Some(null_buf.into());
     } else if array.null_count() == 0 {
-        for (i, offset) in offsets.iter_mut().skip(1).enumerate() {
+        offsets.extend(indices.values().iter().enumerate().map(|(i, index)| {
             if indices.is_valid(i) {
-                let index = indices.value(i).to_usize().ok_or_else(|| {
-                    ArrowError::ComputeError("Cast to usize 
failed".to_string())
-                })?;
-
-                let s: &[u8] = array.value(index).as_ref();
-
-                length_so_far += T::Offset::from_usize(s.len()).unwrap();
+                let s: &[u8] = array.value(index.as_usize()).as_ref();
                 values.extend_from_slice(s);
             }
-            *offset = length_so_far;
-        }
+            T::Offset::usize_as(values.len())
+        }));
         nulls = indices.nulls().map(|b| b.inner().sliced());
     } else {
         let num_bytes = bit_util::ceil(data_len, 8);
 
         let mut null_buf = 
MutableBuffer::new(num_bytes).with_bitset(num_bytes, true);
         let null_slice = null_buf.as_slice_mut();
-
-        for (i, offset) in offsets.iter_mut().skip(1).enumerate() {
-            let index = indices.value(i).to_usize().ok_or_else(|| {
-                ArrowError::ComputeError("Cast to usize failed".to_string())
-            })?;
-
-            if array.is_valid(index) && indices.is_valid(i) {
+        offsets.extend(indices.values().iter().enumerate().map(|(i, index)| {
+            let index = index.as_usize();
+            if indices.is_valid(i) && array.is_valid(index) {

Review Comment:
   this is the actual fix for the bug, right? that `indices.is_valid` is 
checked prior to `array.is_valid`?
   
   ```suggestion
               // check index is valid before using index. The value in
               // NULL index slots may not be within bounds of array
               if indices.is_valid(i) && array.is_valid(index) {
   ```



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