通过变量复制数据框与通过列复制变量

Question

I have been playing with python and understanding the concept of copying a dataframe through the .copy function as opposed to just reassigning it to a variable.

Let's say we have the following data frame: dfx:

   Name        Score1   Score2  Score3        Score4
0  Jack            10  Perfect      10       Perfect
1  Jill            10       10      10  Not Finished
2  Jane            20       10      10             5
3   Tom  Not Finished       15      10             5

dfx2 = dfx.drop("Score1",axis = 1)

dfx2:

   Name   Score2  Score3        Score4
0  Jack  Perfect      10       Perfect
1  Jill       10      10  Not Finished
2  Jane       10      10             5
3   Tom       15      10             5

running dfx again still returns the original dataframe

   Name        Score1   Score2  Score3        Score4
0  Jack            10  Perfect      10       Perfect
1  Jill            10       10      10  Not Finished
2  Jane            20       10      10             5
3   Tom  Not Finished       15      10             5

Shouldn't the reassignment cause the column "Score1" be dropped from the original dataset as well?

However, running the following:

dfx3 = dfx

dfx3

   Name        Score1   Score2  Score3        Score4
0  Jack            10  Perfect      10       Perfect
1  Jill            10       10      10  Not Finished
2  Jane            20       10      10             5
3   Tom  Not Finished       15      10             5

dfx3.loc[0,"Score4"] = "BAD"

dfx3

   Name        Score1   Score2  Score3        Score4
0  Jack            10  Perfect      10           BAD
1  Jill            10       10      10  Not Finished
2  Jane            20       10      10             5
3   Tom  Not Finished       15      10             5

dfx
   Name        Score1   Score2  Score3        Score4
0  Jack            10  Perfect      10           BAD
1  Jill            10       10      10  Not Finished
2  Jane            20       10      10             5
3   Tom  Not Finished       15      10             5

does cause the original dataset to be modified.

Any explanation why a column drop does not modify the original dataset but an element change does change the original? and seems like any change to a column name in an assigned dataset also modifies the original dataset.

Answer 1

你引用dfx3和dfx一个数据帧，如果你想要做的操作上dfx3有类似列dfx的，那么你应该做的副本dfx上dfx3不是他们两个参考相同数据帧。

dfx3 = dfx.copy()