In R I want to add a count variable in dataframe

Question

I have a this dataframe in R:

V1
A
A
C
C
C

I want add a variable like this:

V1 V2
A  1
A  2
C  1
C  2
C  3

Thanks!!

Answer 1

Another dplyr approach:

library(dplyr)

df %>% group_by(V1) %>% mutate(V2 = seq_along(V1))

Answer 2

Does this answer:

> df <- data.frame(V1 = c('A','A','C','C','C'))
> df
  V1
1  A
2  A
3  C
4  C
5  C
> df %>% group_by(V1) %>% mutate(v2 = row_number())
# A tibble: 5 x 2
# Groups:   V1 [2]
  V1       v2
  <fct> <int>
1 A         1
2 A         2
3 C         1
4 C         2
5 C         3
>