Python: how to revert values in a dataframe?

Question

I have a dataframe df composed by two columns x and y. I want to select half of the value of the dataframe and revert the valuese of x and y in this way.

df
         x      y
    0   2557    7
    1   2570    67
    2   2564    27
    3   2581    2578
    4   2571    38
    5   2565    11
    6   2578    41
    7   2577    44
    8   2579    30

dftmp = df  #save original data frame
indeces = np.arange(0, len(df))   # list of index
shuffle(indeces)   # random shuffle
indeces = indeces[0: int(len(indeces) / 2) ]  # take half of random indeces  

df['x'][indeces] = dftmp['y'][indeces]  # x new = y original
df['y'][indeces] = dftmp['x'][indeces]  # y new = x original

I do not know why it changes only the value of y

    df

      x      y
0   2557    2557
1   2570    2570
2   2564    2564
3   2581    2581
4   38      38
5   2565    11
6   41      41
7   2577    44
8   2579    30

It would be of great help if you share your dataframe with us using for instance: **df.to_dict()** — Anton vBR, Jul 27 '17 at 16:47
@emax A quick search gave this: https://stackoverflow.com/questions/27673231/why-should-i-make-a-copy-of-a-data-frame-in-pandas — Anton vBR, Jul 27 '17 at 16:56

score 3 · Answer 1 · answered Jul 27 '17 at 16:51

3

Here's a shorter way of doing that:

df.update(df.sample(frac=0.5).rename(columns={'y': 'x', 'x': 'y'}))

df
Out: 
        x       y
0  2557.0     7.0
1  2570.0    67.0
2  2564.0    27.0
3  2578.0  2581.0
4    38.0  2571.0
5  2565.0    11.0
6    41.0  2578.0
7  2577.0    44.0
8    30.0  2579.0

answered Jul 27 '17 at 16:51

ayhan

70,170
20
182
203

this is very clever! – MaxU - stand with Ukraine Jul 27 '17 at 17:02
@MaxU Thank you. :) – ayhan Jul 27 '17 at 17:03

Python: how to revert values in a dataframe?

1 Answers1