seddonm1 commented on a change in pull request #9233:
URL: https://github.com/apache/arrow/pull/9233#discussion_r575535374
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File path: rust/datafusion/src/physical_plan/hash_aggregate.rs
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@@ -398,97 +405,165 @@ fn group_aggregate_batch(
Ok(accumulators)
}
-/// Create a key `Vec<u8>` that is used as key for the hashmap
-pub(crate) fn create_key(
- group_by_keys: &[ArrayRef],
+/// Appends a sequence of [u8] bytes for the value in `col[row]` to
+/// `vec` to be used as a key into the hash map for a dictionary type
+///
+/// Note that ideally, for dictionary encoded columns, we would be
+/// able to simply use the dictionary idicies themselves (no need to
+/// look up values) or possibly simply build the hash table entirely
+/// on the dictionary indexes.
+///
+/// This aproach would likely work (very) well for the common case,
Review comment:
`aproach` -> `approach`
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