[GitHub] [arrow-rs] jorgecarleitao commented on a change in pull request #341: Fix filter UB and add fast path

[GitBox <gi...@apache.org>]

jorgecarleitao commented on a change in pull request #341:
URL: https://github.com/apache/arrow-rs/pull/341#discussion_r639430911



##########
File path: arrow/src/compute/kernels/filter.rs
##########
@@ -225,38 +248,49 @@ pub fn filter(array: &Array, filter: &BooleanArray) -> Result<ArrayRef> {
     if filter.null_count() > 0 {
         // this greatly simplifies subsequent filtering code
         // now we only have a boolean mask to deal with
-        let array_data = filter.data_ref();
-        let null_bitmap = array_data.null_buffer().unwrap();
-        let mask = filter.values();
-        let offset = filter.offset();
-
-        let new_mask = buffer_bin_and(mask, offset, null_bitmap, offset, filter.len());
-
-        let array_data = ArrayData::builder(DataType::Boolean)
-            .len(filter.len())
-            .add_buffer(new_mask)
-            .build();
-        let filter = BooleanArray::from(array_data);
+        let filter = prep_null_mask_filter(filter);
         // fully qualified syntax, because we have an argument with the same name
         return crate::compute::kernels::filter::filter(array, &filter);
     }
 
     let iter = SlicesIterator::new(filter);
-
-    let mut mutable =
-        MutableArrayData::new(vec![array.data_ref()], false, iter.filter_count);
-    iter.for_each(|(start, end)| mutable.extend(0, start, end));
-    let data = mutable.freeze();
-    Ok(make_array(data))
+    match iter.filter_count {
+        0 => {
+            // return empty
+            Ok(new_empty_array(array.data_type()))
+        }
+        len if len == array.len() => {
+            // return all
+            let data = array.data().clone();
+            Ok(make_array(data))
+        }
+        _ => {
+            // actually filter
+            let mut mutable =
+                MutableArrayData::new(vec![array.data_ref()], false, iter.filter_count);
+            iter.for_each(|(start, end)| mutable.extend(0, start, end));
+            let data = mutable.freeze();
+            Ok(make_array(data))
+        }
+    }
 }
 
 /// Returns a new [RecordBatch] with arrays containing only values matching the filter.
-/// WARNING: the nulls of `filter` are ignored and the value on its slot is considered.
-/// Therefore, it is considered undefined behavior to pass `filter` with null values.
 pub fn filter_record_batch(
     record_batch: &RecordBatch,
     filter: &BooleanArray,

Review comment:
       `predicate`? Removes the need for the full qualified name below (and changing an arguments' name is backward compatible in Rust




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