Convert categorical data in pandas dataframe

I have a dataframe with this type of data (too many columns):

    col1        int64
    col2        int64
    col3        category
    col4        category
    col5        category

Columns seems like this:

    Name: col3, dtype: category
    Categories (8, object): [B, C, E, G, H, N, S, W]

I want to convert all value in columns to integer like this:

    [1, 2, 3, 4, 5, 6, 7, 8]

I solved this for one column by this:

    dataframe['c'] = pandas.Categorical.from_array(dataframe.col3).codes

Now I have two columns in my dataframe - old 'col3' and new 'c' and need to drop old columns.

That's bad practice. It's work but in my dataframe many columns and I don't want do it manually.

How do this pythonic and just cleverly?

First, to convert a Categorical column to its numerical codes, you can do this easier with: dataframe['c']
Further, it is possible to select automatically all columns with a certain dtype in a dataframe using select_dtypes. This way, you can apply above operation on multiple and automatically selected columns.

First making an example dataframe:

    In [75]: df = pd.DataFrame({'col1':[1,2,3,4,5], 'col2':list('abcab'),  'col3':list('ababb')})

    In [76]: df['col2'] = df['col2'].astype('category')

    In [77]: df['col3'] = df['col3'].astype('category')

    In [78]: df.dtypes
    col1       int64
    col2    category
    col3    category
    dtype: object

Then by using select_dtypes to select the columns, and then applying on each of these columns, you can get the following result:

    In [80]: cat_columns = df.select_dtypes(['category']).columns

    In [81]: cat_columns
    Out[81]: Index([u'col2', u'col3'], dtype='object')

    In [83]: df[cat_columns] = df[cat_columns].apply(lambda x:

    In [84]: df
       col1  col2  col3
    0     1     0     0
    1     2     1     1
    2     3     2     0
    3     4     0     1
    4     5     1     1