values = ['y', 'n', '?']
vote_dtype = pandas.api.types.CategoricalDtype(categories=values)
for c in votes.columns[1:]:
    votes[c] = votes[c].astype('object').astype(
        vote_dtype)
democrats = votes[votes['class'] == 'democrat']
republicans = votes[votes['class'] == 'republican']
for vote_col in votes.columns[1:6]:
    pyplot.subplot(1, 2, 1)
    pyplot.hist([1 if x == 'y' else 0 for x in democrats[vote_col]])
    pyplot.title('Democrats: n' + vote_col)
    pyplot.ylabel('count')
    pyplot.subplot(1, 2, 2)
    pyplot.hist([1 if x == 'y' else 0 for x in republicans[vote_col]])
    pyplot.title('Republicans: n' + vote_col)
    pyplot.show()