Counting unique / distinct values by group in a data frame

Question

Let\'s say I have the following data frame:

> myvec
    name order_no
1    Amy       12
2   Jack       14
3   Jack       16
4   Dave       11
5    Amy             


        

Answer 1

Few years old .. although had similar requirement and ended up writing my own solution. Applying here:

 x<-data.frame(
 
 "Name"=c("Amy","Jack","Jack","Dave","Amy","Jack","Tom","Larry","Tom","Dave","Jack","Tom","Amy","Jack"),
 "OrderNo"=c(12,14,16,11,12,16,19,22,19,11,17,20,23,16)
)

table(sub("~.*","",unique(paste(x$Name,x$OrderNo,sep="~",collapse=NULL))))

  Amy  Dave  Jack Larry   Tom
    2     1     3     1     2