Thanks Jim! The problem is not date data. The problem is time. I figured out that I can use chron library and then use this expression times(paste0(t2, ":00")) because my time data are not h:m:s, only h;m. The problem I am trying to figure out is how to implement [times(paste0(t2, ":00"))] on colclasses so that the whole table is converted to correct time format which later can be manipulated Thanks again--EK. [[alternative HTML version deleted]]