Series.
lt
Compare if the current value is less than the other.
>>> df = ps.DataFrame({'a': [1, 2, 3, 4], ... 'b': [1, np.nan, 1, np.nan]}, ... index=['a', 'b', 'c', 'd'], columns=['a', 'b'])
>>> df.a < 1 a False b False c False d False Name: a, dtype: bool
>>> df.b.lt(2) a True b False c True d False Name: b, dtype: bool