Randomly insert NA's values in a pandas dataframe

Question

How can I randomly insert np.nan's in a DataFrame ? Let's say I want 10% null values inside my DataFrame.

My data looks like this :

df = pd.DataFrame(np.random.randn(5, 3), 
                  index=['a', 'b', 'c', 'd', 'e'],
                  columns=['one', 'two', 'three'])

        one       two     three
a  0.695132  1.044791 -1.059536
b -1.075105  0.825776  1.899795
c -0.678980  0.051959 -0.691405
d -0.182928  1.455268 -1.032353
e  0.205094  0.714192 -0.938242

Is there an easy way to insert the null values?

Answer 1

Here's a way to clear exactly 10% of cells (or rather, as close to 10% as can be achieved with the existing data frame's size).

import random
ix = [(row, col) for row in range(df.shape[0]) for col in range(df.shape[1])]
for row, col in random.sample(ix, int(round(.1*len(ix)))):
    df.iat[row, col] = np.nan

Here's a way to clear cells independently with a per-cell probability of 10%.

df = df.mask(np.random.random(df.shape) < .1)