Changing date format to "%d/%m/%Y"

df$ddate <- format(as.Date(df$ddate), "%d/%m/%Y")

df$ddate<-strftime(df$ddate,"%d/%m/%Y")df$bdate<-strftime(strptime(df$bdate,"%d/%m/%y"),"%d/%m/%Y")df$wdate<-strftime(strptime(df$wdate,"%d/%m/%y"),"%d/%m/%Y")

Default R action is to treat strings as factors. Of course, an individual setup may differ from defaults. It's a good practice to change variable values to character, and then convert it to date. I often use chron package - it's nice, simple and what matters the most, it does the job. Only downside of this package lays in time zone handling.

If you don't have chron installed, do:

 install.packages("chron") # load it library(chron) # make dummy data bdate <- c("09/09/09", "12/05/10", "23/2/09") wdate <- c("12/10/09", "05/01/07", "19/7/07") ddate <- c("2009-09-27", "2007-05-18", "2009-09-02") # notice the last argument, it will not allow creation of factors! dtf <- data.frame(id = 1:3, bdate, wdate, ddate, stringsAsFactors = FALSE) # since we have characters, we can do: foo <- transform(dtf, bdate = chron(bdate, format = "d/m/Y"), wdate = chron(wdate, format = "d/m/Y"), ddate = chron(ddate, format = "y-m-d")) # check the classes sapply(foo, class) # $id # [1] "integer" # $bdate # [1] "dates" "times" # $wdate # [1] "dates" "times" # $ddate # [1] "dates" "times"

C'est ca... it should do the trick...