import numpy as np import pandas as pd arr = np.random.randn(4, 4) df = pd.DataFrame(arr) df[4] = "foo" df.iloc(axis=1)[2] = 3 >>> df 0 1 2 3 4 0 -0.042240 2.894031 0.086813 0.808991 foo 1 0.141410 1.998173 0.730306 -0.779878 foo 2 3.000000 3.000000 3.000000 3.000000 3 3 0.270897 1.830372 0.533242 -0.147240 foo 

>>> df 0 1 2 3 4 0 -0.042240 2.894031 3 0.808991 foo 1 0.141410 1.998173 3 -0.779878 foo 2 1.611364 1.459234 3 0.572484 foo 3 0.270897 1.830372 3 -0.147240 foo