Create a new column that shows the occurence number of item in dataframe

Question

I have a dataframe that contains a column that look like this

Name 
A
A
B
B
C

I want to append a column to this dataframe where it contains the occurrence number of the item in Name

Name  New_Column
A     1
A     2
B     1
B     2
C     1

So far, I can just turn Name column into a list, then loop over it and create the new_column, but is there a more straightforward way to do this directly in pandas?

`df.assign(New_Column=df.groupby('Name').cumcount() + 1)` Looking for dup. — piRSquared, Dec 06 '18 at 16:19
thank you @piRSquared, it works, if you want, you can leave an answer and I can mark it as accepted — Jason, Dec 06 '18 at 16:26
Thx @Jason I know this is a duplicate question. I'm going to find it and mark it as such. It is what we're supposed to do anyway (-: — piRSquared, Dec 06 '18 at 16:28

score 4 · Accepted Answer · answered Dec 06 '18 at 16:33

`groupby` and `cumcount`

cumcounts sole purpose is to increment each group separately. If you add one to the result and assign it as a new column:

df.assign(New_Column=df.groupby('Name').cumcount() + 1)

  Name  New_Column
0    A           1
1    A           2
2    B           1
3    B           2
4    C           1

Create a new column that shows the occurence number of item in dataframe

1 Answers1

groupby and cumcount

`groupby` and `cumcount`