Counting unique / distinct values by group in a data frame

Question

I have a dataframe: > myvec name order_no 1 Nehal 12 2 sejal 14 3 sejal 16 4 shyam 11 5 Nehal 12 6 Sejal 16 7 Ram 19 For each name how to count the distinct order no. Value. I am expecting this output: name number_of_distinct_orders Neha 2 Sejal 3 Shyam 1 Ram 1 Select the correct answer from above options

Answer 1

If you have plyr package then use this: ddply(myvec,~name,summarise,number_of_distinct_orders=length(unique(order_no))) else use data.table approach library(data.table) DT <- data.table(myvec) DT[, .(number_of_distinct_orders = length(unique(order_no))), by = name]