Group by dictionary encoded arrays.

Casting a table column consumes memory, but casting an in-memory dataset field appears to have no performance impact. This could simplify and optimize the functional use cases which dictionary arrays do not support.

Binary only preview builds.

.github/workflows/build.yml

@@ -16,7 +16,7 @@ jobs:
         arrow-version: ['']
         include:
         - python-version: 3.x
-          arrow-version: '--pre '
+          arrow-version: '--pre --only-binary :all: '
     steps:
     - uses: actions/checkout@v4
     - uses: actions/setup-python@v5

graphique/core.py

@@ -421,13 +421,13 @@ def group(self, *names: str, counts: str = '', **funcs: Sequence[Agg]) -> pa.Tab
         """
         prefix = 'hash_' if names else ''
         aggs = [agg.astuple(prefix + func) for func in funcs for agg in funcs[func]]
-        columns = list(names) + [agg[0] for agg in aggs]
+        columns = {
+            name: pc.field(name).cast(Column.scalar_type(self.schema.field(name)))
+            for name in list(names) + [agg[0] for agg in aggs]
+        }
         if counts:
             aggs.append(([], 'hash_count_all', None, counts))
-        if isinstance(self, pa.Table):
-            decl = Declaration('table_source', self.unify_dictionaries())
-        else:
-            decl = Declaration.scan(self, columns=columns)
+        decl = Declaration.scan(ds.dataset(self) if isinstance(self, pa.Table) else self, columns)
         return decl.aggregate(aggs, names).to_table(use_threads=False)
 
     def aggregate(self, counts: str = '', **funcs: Sequence[Agg]) -> dict:

graphique/interface.py

@@ -249,8 +249,7 @@ def group(
         table, aggs = self.table, dict(aggregate)
         refs = {agg.name for values in aggs.values() for agg in values}
         fragments = set(T.fragment_keys(self.table))
-        dicts = (pa.types.is_dictionary(table.schema.field(name).type) for name in set(by) | refs)
-        if isinstance(table, ds.Scanner) or any(dicts):
+        if isinstance(table, ds.Scanner):
             table = self.select(info)
         if fragments and set(by) <= fragments:
             if set(by) == fragments: