Iteration over two grouped data frames

[bkamins]

@uferc

for (i, (gdf, gdf_c)) in enumerate(zip(groupby(df, :var, sort = true)), groupby(df2, :var, sort = true))

Use

for (i, (gdf, gdf_c)) in enumerate(zip(groupby(df, :var, sort = true), groupby(df2, :var, sort = true)))