python - Slicing a Pandas DataFrame into a new DataFrame

Question

I would like to slice a DataFrame with a Boolean index obtaining a copy, and then do stuff on that copy independently of the original DataFrame.

Judging from this answer, selecting with .loc using a Boolean array will hand me back a copy, but then, if I try to change the copy, SettingWithCopyWarning gets in the way. Would this then be the correct way:

import numpy as np
import pandas as pd
d1 = pd.DataFrame(np.random.randn(10, 5), columns=['a', 'b', 'c', 'd', 'e'])
# create a new dataframe from the sliced copy
d2 = pd.DataFrame(d1.loc[d1.a > 1, :])
# do stuff with d2, keep d1 unchanged

Answer 1

You need copy with boolean indexing, new DataFrame constructor is not necessary:

d2 = d1[d1.a > 1].copy()

Explanation of warning:

If you modify values in d2 later you will find that the modifications do not propagate back to the original data (d1), and that Pandas does warning.