First of all I would like to say thanks to everyone for sharing valuable information, now I can able to do that if date column datatype is “Factor” but by default the date column datatype is “POSIXct” in R ,so whenever I want apply stfrtime function with sqldf package ,do I need to convert the date datatype to factor ??? or is there any alternative way?
Manu. On Fri, Sep 16, 2016 at 9:08 PM, peter dalgaard <[email protected]> wrote: > > On 16 Sep 2016, at 15:23 , PIKAL Petr <[email protected]> wrote: > > > Hi Peter > > > > The devil is in detail > > > > Data from OP had different format and was transferred to Date object by > as.Date, which results in incorrect values (and NA if not transferred) > > df <- data.frame(Date = c("2013/05/25","2013/05/28"," > 2013/05/31","2013/06/01","2013/06/02", > > "2013/06/05","2013/06/07"), Quantity = c(9,1,15,4,5,17,18)) > > df$Date<-as.Date(df$Date) > > cbind(df, sqldf("select strftime( '%m', Date) from df")) > > > > To be fair, he actually used as.Date(...., "%Y/%m/%d"), so the values were > in fact correct. The issue lay in the conversion to integer. > > I can't figure out how those integers are interpreted, though: > > > df <- data.frame(date=c(0,1000,2000)) > > cbind(df, sqldf("select strftime( '%Y-%m-%d', date) from df")) > date strftime( '%Y-%m-%d', date) > 1 0 -471-11-24 > 2 1000 -471-08-20 > 3 2000 -470-05-16 > > so the Epoch is nothing sensible and negative years are more than a > thousand days?? > > > -- > Peter Dalgaard, Professor, > Center for Statistics, Copenhagen Business School > Solbjerg Plads 3, 2000 Frederiksberg, Denmark > Phone: (+45)38153501 > Office: A 4.23 > Email: [email protected] Priv: [email protected] > > -- Thanks, Manohar Reddy P +91-9705302062. [[alternative HTML version deleted]] ______________________________________________ [email protected] mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
