Pandas - make a column dtype object or Factor

Question

In pandas, how can I convert a column of a DataFrame into dtype object? Or better yet, into a factor? (For those who speak R, in Python, how do I as.factor()?)

Also, what's the difference between pandas.Factor and pandas.Categorical?

Answer 1

You can use the astype method to cast a Series (one column):

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

Or the entire DataFrame:

df = df.astype(object) 

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Update

Since version 0.15, you can use the category datatype in a Series/column:

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

Note: pd.Factor was been deprecated and has been removed in favor of pd.Categorical.

Answer 2

There's also pd.factorize function to use:

# use the df data from @herrfz  In [150]: pd.factorize(df.b) Out[150]: (array([0, 1, 0, 1, 2]), array(['yes', 'no', 'absent'], dtype=object)) In [152]: df['c'] = pd.factorize(df.b)[0]  In [153]: df Out[153]:     a       b  c 0  1     yes  0 1  2      no  1 2  3     yes  0 3  4      no  1 4  5  absent  2