Thank you very much. It worked great with the testdata. I have one more questionto to ask. As my data is incomplete, sometimes Thu is also missing, then I have no other options but to pick Sat instead, and if Sat is also missing, then my best possible option is to pick Wed, and etc. Bascially I have to pick a day as the data for that week starting from Friday following this order:
Fri--> (if no Fri) Thu--> (if no Thu) Sat--> (if no Sat) Wed --> (if no Wed) Sun --> (if no Sun) Tue -->(if no Tue) Mon. In this sense, I have to write a loop if command, right? Could you please help me with that? Again thanks a lot. testdata$date = as.Date(testdata$date,"%m/%d/%Y") Thudat = subset(testdata,day=="Thu") Fridat = subset(testdata,day=="Fri") Friday_dates = Thudat$date+1 Friday_info = NULL for(i in 1:length(Friday_dates)){ temp = subset(Fridat,date==Friday_dates[i]) # select the Friday dates from Fridat if(nrow(temp)>0){ # if that Friday date value exists in Friday Friday_info = rbind(Friday_info,temp[nrow(temp),]) # by saying nrow(temp) with the data organized chronologically already, you don't have to add an additional if statement for multiple measurements in the same day. } else { # if that Friday date value doesn't exist in Fridat Friday_info = rbind(Friday_info,Thudat[i,]) # choosing the date from Thudat instead. } } -- View this message in context: http://r.789695.n4.nabble.com/How-to-extract-Friday-data-from-daily-data-tp3029050p3029328.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list 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.