How to remove rows that have only 1 combination for a given ID

Question

I have a dataframe like this

ID <- c(\"A\",\"A\",\"A\",\"B\",\"B\",\"C\",\"C\")
Measurement <- c (\"Length\",\"Breadth\",\"Breadth\",\"Breadth\",\"Leng         


        

Answer 1

Using data.table:

library(data.table)
DT <- data.table(df)
DT[, Count := length(unique(Measurement)), ID][Count > 1]

Edit

Alternatively, a much better one-liner suggested by @DavidArenburg:

setDT(df)[, if(uniqueN(Measurement) > 1) .SD, by = ID]