feat(datafusion): implement Count operation

ibis/backends/datafusion/compiler.py

@@ -331,6 +331,16 @@ def mod(op, expr):
     return translate(op.left) % translate(op.right)
 
 
+@translate.register(ops.Count)
+def count(op, expr):
+    op_arg = op.arg
+    if isinstance(op_arg, ir.TableExpr):
+        arg = df.literal(1)
+    else:
+        arg = translate(op_arg)
+    return df.functions.count(arg)
+
+
 @translate.register(ops.Sum)
 def sum(op, expr):
     arg = translate(op.arg)

ibis/backends/tests/test_aggregation.py

@@ -471,7 +471,6 @@ def test_binds_are_cast(alltypes):
     expr.execute()
 
 
-@pytest.mark.notimpl(["datafusion"])
 def test_agg_sort(alltypes):
     query = alltypes.aggregate(count=alltypes.count())
     query = query.sort_by(alltypes.year)

ibis/backends/tests/test_generic.py

@@ -410,6 +410,8 @@ def test_table_info(alltypes):
     alltypes.info(buf=buf)
 
     info_str = buf.getvalue()
-    assert info_str is not None
+    schema = alltypes.schema()
+
     assert "Nulls" in info_str
-    assert all(str(type) in info_str for type in alltypes.schema().types)
+    assert all(str(type) in info_str for type in schema.types)
+    assert all(name in info_str for name in schema.names)