Dear R Community, I am new to R, and have a question that I suspect may be quite simple but is proving a formidable roadblock for me. I have a large data set that includes water-quality measurements collected over many 24-hour periods. The date and time of sample collection are in a combined Date/Time field in the format yyyy-mm-dd hh:mm:ss. I need to be able to subset the data for analysis of different date and time windows. Thus far, I have tried casting the Date/Time field using several approaches, such as:
DataSet$NewDateTime <- strptime(DataSet$DateTime, '%Y-%m-%d %H:%M:%S') DataSet$NewDateTime <- as.POSIXlt(strptime(DataSet$DateTime, '%Y-%m-%d %H:%M:S')) These instructions seem to cast the NewDateTime field correctly (at least it appears to be in the correct format, and I assume R sees the field as a date and a time) but I am then unable to subset the data using instructions such as: with(DataSet, subset(DataSet, DataSet$NewDateTime < '2004-08-05 14:15:00')) DataSubset <- subset(DataSet, DataSet$NewDateTime < '2004-08-05 14:00:00', select = DataSet) I have tried also separating the date and time fields in the input file, and casting with instructions such as: DataSet$NewTime <- strptime(DataSet$Time, '%H:%M:%S') DataSet$NewTime <- as.POSIXct(strptime(DataSet$Time, '%H:%M:%S')) but these seem to generate a NewTime field that contains today's date + the time data, and also will not subset based on date/time. I appreciate greatly any help and advice, Steve -- View this message in context: http://r.789695.n4.nabble.com/help-subsetting-data-based-on-date-AND-time-tp3799933p3799933.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.
