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rdataframeunique

Count unique values in R and display in column

I have this dataframe, and I would like to count the unique values in column A and display them in Column D

So the if else function should look at column A and ad 1 for each new unique user

> DF_Have <- data.frame(A=c(1,2,2,3,3), B=1:5*10, C=1:5*100)
> DF_Have
   A  B   C
1: 1 10 100
2: 2 20 200
3: 2 30 300
4: 3 40 400
5: 3 50 500


> DF_Want
   A  B   C   D
1: 1 10 100   1
2: 2 20 200   2
3: 2 30 300   2
4: 3 40 400   3
5: 3 50 500   3
Solution 
  • library(data.table)
DF_Have$D <- rleid(DF_Have$A)
DF_Have
#  A  B   C D
#1 1 10 100 1
#2 2 20 200 2
#3 2 30 300 2
#4 3 40 400 3
#5 3 50 500 3

    another option without need of any external package is( provided DF_Have$A is ordered) 

    DF_Have$D <- cumsum(!duplicated(DF_Have$A))