大熊猫平均值数据框更改初始数据框

Question

I have been stumbling upon a problem and have no idea why it behaves like that. I have pandas DataFrame with hourly values and wanted to make a new DataFrame out of this with the monthly mean values for each hour. This is one part of the code I used:

flussmonthly=fluss2 
flussmonthly['2015-06-01 00:00:00' : '2015-06-30 23:00:00']=fluss2['2015-06-01 00:00:00' : '2015-06-30 23:00:00'].mean()

where fluss2 is the initial DataFrame with the hourly values and flussmonthly should in the end be the DataFrame with the monthly mean values. however, whenever I apply this code the DataFrame flussmonthly has the average value of this month for each hour, but also the DataFrame fluss2 has. I have no idea why. How can it be that also the DataFrame fluss2 changes?

Answer 1

When you do:

flussmonthly=fluss2

You are not copying the data frame, but just copying the reference . If you want flussmonthly to be a different, independent data frame containing the same data as fluss2 the you should do:

flussmonthly = fluss2.copy()

Then changing flussmonthly will not affect fluss2 .