[R] Identifying duplicate rows?

[kborgmann]

Hi,
I am trying to identify duplicate values in a column in a date frame.  The
duplicated function identifies the duplicate rows in the data frame but it
only does this for the second record, not both records. Is there a way to
mark both rows in the data frame as TRUE? 
dfA$dups<-duplicated(dfA$Value)
dfA
Site	State Value dups
929	VA	73 FALSE
929	VA	73  TRUE
930	VA	76 FALSE
930	VA	76 TRUE
931	VA	74 FALSE
932	VA	75 FALSE

But I would like this
Site	State Value dups
929	VA	73 TRUE
929	VA	73  TRUE
930	VA	76 TRUE
930	VA	76 TRUE
931	VA	74 FALSE
932	VA	75 FALSE

Thank you for your replies! 
Still on the learning curve,
Kathi



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