Keep rows in a dataset if one value in a column is duplicated

Hi,

I have a data set of observations by either one person or a pair of people.
I want to only keep the pair observations, and was using the code below
until it gave me the error " $ operator is invalid for atomic vectors". I am
just beginning to learn R, so I apologize if the code is really rough.

Basically I want to keep all the rows in the data set for which the value of
"Pairiddups" is TRUE. How do I do it? And how do I get past the error?

Thank you so much,
Diana

PairID<-c(Health2$pairid)

duplicated(PairID, incomparables=TRUE, fromLast=TRUE)

PairIDdup=duplicated(PairID)
cbind(PairID, PairIDdup)
PairID[which(PairIDdup)]

PairIDDuplicates<-PairID%in%PairID[which(PairIDdup)]
PairIDs<-cbind(PairID, PairIDDuplicates)

colnames(PairIDs)<-c("Pairid","Pairiddups")

Health2PairsOnly<-PairIDs[ which(PairIDs$Pairiddups=='TRUE'), ]



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