How to insert -1 to every 11-th position in the dataframe?

Question

I have the following dataframe : On every 11th row i would like to insert -1. Tried a few suggestion but did not get what i expected.

Show what you tried as properly formatted code in the question. — Michael Butscher, Jan 07 '21 at 00:11
[It works just like Python list slicing](https://stackoverflow.com/a/31593712/8881141): `df.loc[::11, "column name"] -= 1` — Mr. T, Jan 07 '21 at 00:13

score 0 · Accepted Answer · answered Jan 07 '21 at 00:20

Maybe you could use pandas.DataFrame.iloc:

>>> import pandas as pd
>>> d = {'%UNWEIGHTED_ILI': [0.184361, 0.527357, 0.330384, 0.100392,
                             0.491726, 0.433408, 0.117853, 0.129628,
                             0.204399, 0.342965, 0.123456, 0.976543]}
>>> df = pd.DataFrame(data=d)
>>> df
    %UNWEIGHTED_ILI
0          0.184361
1          0.527357
2          0.330384
3          0.100392
4          0.491726
5          0.433408
6          0.117853
7          0.129628
8          0.204399
9          0.342965
10         0.123456
11         0.976543
>>> df.iloc[::11, :] -= 1
>>> # df.iloc[11::11, :] -= 1 If you don't want -1 to be added to the first row
>>> df
    %UNWEIGHTED_ILI
0         -0.815639
1          0.527357
2          0.330384
3          0.100392
4          0.491726
5          0.433408
6          0.117853
7          0.129628
8          0.204399
9          0.342965
10         0.123456
11        -0.023457

I would like to insert a -1 rather. Not add to the existing data. And also it has to be for every 11th row. Thanks for your answer. — CD_NS, Jan 07 '21 at 00:25

How to insert -1 to every 11-th position in the dataframe?

1 Answers1