Pandas DataFrame column with increasing counter by values in another column

Question

I have a data frame with a column having various letters ordered.

I want to create a column that counts increasingly the number of times a letter is repeated at each new row:

Letters     Counter
A           1
A           2
A           3
B           1
C           1
C           2
D           1
D           2
D           3
D           4

Is there a way to avoid a loop?

BENY · Accepted Answer · 2020-05-17 16:10:09Z

1

We have cumcount

df['count']=df.groupby('Letters').cumcount()+1
df
  Letters  Counter  count
0       A        1      1
1       A        2      2
2       A        3      3
3       B        1      1
4       C        1      1
5       C        2      2
6       D        1      1
7       D        2      2
8       D        3      3
9       D        4      4

answered May 17, 2020 at 16:10

BENY

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