I was having a similar problem, then found that a previous format statement had changed the column with the dash in front of it to a string. I changed the column back into floats, and the dash worked fine, no longer giving me a unary operator error. -- View this message in context: http://n4.nabble.com/Error-in-class-invalid-argument-to-unary-operator-tp884858p1594282.html Sent from the R help mailing list archive at Nabble.com.