Hi, On Fri, Dec 24, 2010 at 5:45 AM, Ali Salekfard <salekf...@googlemail.com> wrote: [snip] > I have a data frame that contains mapping rules in this way: > > ACCOUNT, RULE COLUMNS, Effective Date > > > The dataframe comes from a database that stores all dates. What I would like > to do is to create a data frame with only the most recent rule for each
Assuming that "Effective Date" is a date class (you can use str(yourdataframe) you tell): with(YourDataFrame, tapply(`Effective Date`, `RULE COLUMNS`, which.max)) this will return the location of the maximum `Effective Date` If you want the actual value, rather than the location: with(YourDataFrame, tapply(`Effective Date`, `RULE COLUMNS`, function(x) x[which.max(x)])) should do the trick (assuming Effective Date is a date class, not character). By the way, you will find your life more convenient if you avoid object or column names with spaces or special characters. Cheers, Josh > account. In traditional programming languages I would loop through each > account find the most recent rule(s) and fill up my updated data frame. > > Does anyone have any better idea to use R's magic (Its syntax is still > magical to me) for this problem? > > By the way the list of rules is quite extensive (144643 lines to be > precise), and there are usually 1-3 most recent rules (rows) for each > account. > > Thanks. > > [[alternative HTML version deleted]] > > ______________________________________________ > 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. > -- Joshua Wiley Ph.D. Student, Health Psychology University of California, Los Angeles http://www.joshuawiley.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.
