If I try to compare two Series with different categories I get an error:
a = pd.Categorical([1, 2, 3])
b = pd.Categorical([4, 5, 3])
df = pd.DataFrame([a, b], columns=['a', 'b'])
a b
0 1 4
1 2 5
2 3 3
df.a == df.b
# TypeError: Categoricals can only be compared if 'categories' are the same.
What is the best way to update categories in both Series? Thank you!
My solution:
df['b'] = df.b.cat.add_categories(df.a.cat.categories.difference(df.b.cat.categories))
df['a'] = df.a.cat.add_categories(df.b.cat.categories.difference(df.a.cat.categories))
df.a == df.b
Output:
0 False
1 False
2 True
dtype: bool
One idea with union_categoricals:
from pandas.api.types import union_categoricals
union = union_categoricals([df.a, df.b]).categories
df['a'] = df.a.cat.set_categories(union)
df['b'] = df.b.cat.set_categories(union)
print (df.a == df.b)
0 False
1 False
2 True
dtype: bool