Assign unique ID based on two columns
We can do this in base R
without doing any group by operation
df$ID <- cumsum(!duplicated(df[1:2]))
df
# School Student Year ID
#1 A 10 1999 1
#2 A 10 2000 1
#3 A 20 1999 2
#4 A 20 2000 2
#5 A 20 2001 2
#6 B 10 1999 3
#7 B 10 2000 3
NOTE: Assuming that 'School' and 'Student' are ordered
Or using tidyverse
library(dplyr)
df %>%
mutate(ID = group_indices_(df, .dots=c("School", "Student")))
# School Student Year ID
#1 A 10 1999 1
#2 A 10 2000 1
#3 A 20 1999 2
#4 A 20 2000 2
#5 A 20 2001 2
#6 B 10 1999 3
#7 B 10 2000 3
As @radek mentioned, in the recent version (dplyr_0.8.0
), we get the notification that group_indices_
is deprecated, instead use group_indices
df %>%
mutate(ID = group_indices(., School, Student))
Group by School and Student, then assign group id to ID
variable.
library('data.table')
df[, ID := .GRP, by = .(School, Student)]
# School Student Year ID
# 1: A 10 1999 1
# 2: A 10 2000 1
# 3: A 20 1999 2
# 4: A 20 2000 2
# 5: A 20 2001 2
# 6: B 10 1999 3
# 7: B 10 2000 3
Data:
df <- fread('School Student Year
A 10 1999
A 10 2000
A 20 1999
A 20 2000
A 20 2001
B 10 1999
B 10 2000')