Pandas shows SettingWithCopyWarning after train_test_split [duplicate]

Answer 1

Pandas spits out this warning too aggressively in general, you can see a good discussion here: How to deal with SettingWithCopyWarning in Pandas?

But if I'm confident that my code works as expected, I just use:

pd.options.mode.chained_assignment = None

at the top of my file. You'll always be able to tell if you're not updating your df because whatever you thought you did won't be there.

Answer 2

You can workaround it as follows:

In [16]: Xt = Xt.copy()

In [17]: Xt.iloc[0,0]=6

In [18]: Xt
Out[18]:
   A  B
0  6  2
2  7  3
1  5  5

In [19]: X
Out[19]:
   A   B
0  2   2     # <--- NOTE: the value in the original DF has NOT been changed
1  5   5
2  7   3
3  8  51
4  9   5

Alternatively you can use numpy.split(...) method

Answer 3

Another option is to reset the is_copy flat but it seems this is a bug of the train_test_split function.

Xt.is_copy=None