Grouping by two columns mixes up the keys

[ondraz]

Grouping by two columns mixes the keys up. See below. Aggregated output shows dict with 'grp_1': 'b', 'grp_2': 'c' . That combination of keys is not present in original list_dicts data.

from clumper import Clumper

list_dicts = [
    {'grp_1': 'a', 'grp_2': 'a', 'a': 6},
    {'grp_1': 'a', 'grp_2': 'b', 'a': 7},
    {'grp_1': 'a', 'grp_2': 'c', 'a': 5},
    {'grp_1': 'b', 'grp_2': 'a', 'a': 2},
    {'grp_1': 'b', 'grp_2': 'b', 'a': 4},
]

(Clumper(list_dicts)
  .group_by('grp_1', 'grp_2')
  .agg(c=('a', 'count'),
       s=('a', 'sum'),
       m=('a', 'mean'))
  .collect()
)

# output
[{'grp_1': 'b', 'grp_2': 'b', 'c': 1, 's': 4, 'm': 4},
 {'grp_1': 'b', 'grp_2': 'a', 'c': 1, 's': 7, 'm': 7},
 {'grp_1': 'b', 'grp_2': 'c', 'c': 1, 's': 2, 'm': 2},     # this key combination is not present in list_dicts
 {'grp_1': 'a', 'grp_2': 'b', 'c': 1, 's': 5, 'm': 5},
 {'grp_1': 'a', 'grp_2': 'c', 'c': 1, 's': 6, 'm': 6}]     # 'grp_1': 'a', 'grp_2': 'a' is missing here

python 3.9.7, clumper 0.2.15