Swapping rows within the same pandas dataframe

问题

I'm trying to swap the rows within the same DataFrame in pandas.

I've tried running

a = pd.DataFrame(data = [[1,2],[3,4]], index=range(2), columns = ['A', 'B'])
b, c = a.iloc[0], a.iloc[1]
a.iloc[0], a.iloc[1] = c, b

but I just end up with both the rows showing the values for the second row (3,4).

Even the variables b and c are now both assigned to 3 and 4 even though I did not assign them again. Am I doing something wrong?

回答1:

Use a temporary varaible to store the value using .copy(), because you are changing the values while assigning them on chain i.e. Unless you use copy the data will be changed directly.

a = pd.DataFrame(data = [[1,2],[3,4]], index=range(2), columns = ['A', 'B'])
b, c = a.iloc[0], a.iloc[1]


temp = a.iloc[0].copy()
a.iloc[0] = c
a.iloc[1] = temp

Or you can directly use copy like

a = pd.DataFrame(data = [[1,2],[3,4]], index=range(2), columns = ['A', 'B'])
b, c = a.iloc[0].copy(), a.iloc[1].copy()
a.iloc[0],a.iloc[1] = c,b

回答2:

In this way, it can be extrapolated to more complex situations:

    a = pd.DataFrame(data = [[1,2],[3,4]], index=range(2), columns = ['A', 'B'])
    rows = a.index.tolist()
    rows = rows[-1:]+rows[:-1]
    a=a.loc[rows]

来源：https://stackoverflow.com/questions/46890972/swapping-rows-within-the-same-pandas-dataframe