Question

I have the following data.frame

   x y   
1 t1 5                  
2 t2 2   
3 t2 7  
4 t3 9  
5 t1 6 

how add a column with the occurence number of the value in the first column like below ?:

   x y occ  
1 t1 5 1  
2 t2 2 1  
3 t2 7 2  
4 t3 9 1  
5 t1 6 2  

Answer 1

Not 100% sure but is this what you mean?

> my.df <- data.frame(x=c("t1","t2","t2","t3","t1"), y=c(5,2,7,9,6))
> my.df <- data.frame(x=my.df$x,
+                     y=my.df$y,
+                     occ=sapply(1:nrow(my.df), function(i) sum(my.df$x[1:i] == my.df$x[i])))

> my.df
   x y occ
1 t1 5   1
2 t2 2   1
3 t2 7   2
4 t3 9   1
5 t1 6   2