Cumulative count of each value

Question

I want to create a cumulative counter of the number of times each value appears.

e.g. say I have the column:

id  
1  
2  
3  
2  
2  
1  
2  
3

This would become:

id   count  
1     1  
2     1  
3     1  
2     2  
2     3  
1     2  
2     4  
3     2  

etc...

Answer 1

The dplyr way:

library(dplyr)

foo <- data.frame(id=c(1, 2, 3, 2, 2, 1, 2, 3))
foo <- foo %>% group_by(id) %>% mutate(count=row_number())
foo

# A tibble: 8 x 2
# Groups:   id [3]
     id count
  <dbl> <int>
1     1     1
2     2     1
3     3     1
4     2     2
5     2     3
6     1     2
7     2     4
8     3     2

That ends up grouped by id. If you want it not grouped, add %>% ungroup().