Assign a unique identifier based on two columns

Question

I have a dataframe (df) that looks like this:

School Student  Year  
A         10    1999
A         10    2000
A         20    1999
A         20    2000
A         20    2001
B         10    1999
B         10    2000

And I would like to create a person column IDso that df looks like this:

ID School Student  Year  
1   A         10    1999
1   A         10    2000
2   A         20    1999
2   A         20    2000
2   A         20    2001
3   B         10    1999
3   B         10    2000

In other words, the variable IDindicates in which staff it is in the data set, taking into account both the number of students and school membership (here we have only 3 students).

I did df$ID <- df$Studentand tried to request a +1 if it c("School", "Student)was unique. He does not work. Help evaluate.

Answer 1

We can do this base Rwithout any operation group

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

. , "" ""

---

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

Answer 2

, ID.

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

:

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')