Fixing groupby axis.

libcodonusage/__init__.py

 __copyright__ = "Copyright (C) 2022-2023 Blaise Li, Marie Anselmet"
 __licence__ = "GNU GPLv3"
-__version__ = "0.28.3"
+__version__ = "0.28.4"
 from .libcodonusage import (
     aa2colour,
     aa_usage,

libcodonusage/libcodonusage.py

@@ -552,7 +552,7 @@ def group_codons_by_class(
     # getattr accesses the method whose name is in argument *mode*
     # and this method is called to get the result of the groupby operation.
     codon_counts_grouped = getattr(
-        codon_counts_pre_group.groupby(level=["aa", "codon"]),
+        codon_counts_pre_group.groupby(level=["aa", "codon"], axis=1),
         mode)()
     if keep_only_groups:
         return codon_counts_grouped