Create variable with count of 1, 2,3 ,4 in R

Question

See below example, I need to create a new column called N_Count for each ID*Value. Searched but without good luck.

ID     Value     Count   N_Count
1        a         2     1
1        a         2     2
1        b         1     1
2        a         2     1
2        a         2     2
3        a         1     3 
3        b         3     1
3        b         3     2
3        b         3     3

Answer 1

One possible solution can be as:

library(dplyr)
df %>%
group_by(ID, Value) %>%
  mutate(n_Count = row_number())

# # A tibble: 9 x 4
# # Groups: ID, Value [5]
#      ID Value Count   n_Count
#     <int> <chr> <int>   <int>
# 1     1 a         2       1
# 2     1 a         2       2
# 3     1 b         1       1
# 4     2 a         2       1
# 5     2 a         2       2
# 6     3 a         1       1
# 7     3 b         3       1
# 8     3 b         3       2
# 9     3 b         3       3

Data

df <- read.table(text =
"ID     Value     Count   
1        a         2     
1        a         2     
1        b         1     
2        a         2     
2        a         2     
3        a         1      
3        b         3     
3        b         3     
3        b         3",
header = TRUE, stringsAsFactors = FALSE)