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

my.1 <- table(myvec)

my.1[my.1 != 0] <- 1

rowSums(my.1)