pandas randomly replace k percent

Question

having a simple pandas data frame with 2 columns e.g. id and value where value is either 0 or 1 I would like

Answer 1

you can probably use numpy.random.choice:

>>> idx = df.index[df.value==1]
>>> df.loc[np.random.choice(idx, size=idx.size/10, replace=False)].value = 0