Within ID, check for matches/differences

Question

I have a large dataset, over 1.5 million rows, from 600k unique subjects, so a number of subjects have multiple rows. I am trying to find the cases where the one of the subj

Answer 1

DOBError <- function(data){

     count <- unlist(lapply(split(test, test$ID), 
        function(x)length(unique(x$DOB))))

     return(names(count)[count > 1])

}


DOBError(data)

[1] "2"