alamb commented on code in PR #6178:
URL: https://github.com/apache/arrow-rs/pull/6178#discussion_r1709949954


##########
arrow-select/src/filter.rs:
##########
@@ -707,6 +710,62 @@ fn filter_byte_view<T: ByteViewType>(
     GenericByteViewArray::from(unsafe { builder.build_unchecked() })
 }
 
+fn filter_fixed_size_binary(
+    array: &FixedSizeBinaryArray,
+    predicate: &FilterPredicate,
+) -> FixedSizeBinaryArray {
+    let values: &[u8] = array.values();
+    let value_length = array.value_length() as usize;
+    let calcualte_offset_from_index = |index: usize| index * value_length;
+    let buffer = match &predicate.strategy {
+        IterationStrategy::SlicesIterator => {
+            let mut buffer = MutableBuffer::with_capacity(predicate.count * 
value_length);
+            for (start, end) in SlicesIterator::new(&predicate.filter) {
+                buffer.extend_from_slice(
+                    
&values[calcualte_offset_from_index(start)..calcualte_offset_from_index(end)],
+                );
+            }
+            buffer
+        }
+        IterationStrategy::Slices(slices) => {
+            let mut buffer = MutableBuffer::with_capacity(predicate.count * 
value_length);
+            for (start, end) in slices {
+                buffer.extend_from_slice(
+                    
&values[calcualte_offset_from_index(*start)..calcualte_offset_from_index(*end)],
+                );
+            }
+            buffer
+        }
+        IterationStrategy::IndexIterator => {
+            let iter = IndexIterator::new(&predicate.filter, 
predicate.count).map(|x| {
+                
&values[calcualte_offset_from_index(x)..calcualte_offset_from_index(x + 1)]
+            });
+
+            // SAFETY: IndexIterator is trusted length
+            unsafe { MutableBuffer::from_trusted_len_iter_slice_u8(iter, 
value_length) }

Review Comment:
   > I will use these two methods to implement and compare performance, 
tomorrow or the day after tomorrow.
   
   Thank you @chloro-pn and @tustvold (also thank you for writing the 
benchmarks that can show it) -- I think this is the best approach so that we 
can see what the actual impact on performance is rather than theorizing what 
the compiler might / might not do



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