when is typecasting of objects to category useful pandas code example

Example 1: how to convert each string to a category or int in python dataframe

In [3]: df = pd.DataFrame({"A": ["a", "b", "c", "a"]})

In [4]: df["B"] = df["A"].astype('category')

In [5]: df
Out[5]: 
   A  B
0  a  a
1  b  b
2  c  c
3  a  a

Example 2: how to make a column a factor in pandas

df['col_name'] = df['col_name'].astype('category')