Hi Michael On 1 Dec 2004 at 11:50, michael watson (IAH-C) wrote:
> Hi > > I have used merge() to merge two data frames, very much like > performing a SQL join. Now I want to do a few different SQL-style > things and I wondered if there were functions to do it... > > Is there a "group by" style function? For example if I merge() two > data frames and end up with multiple rows for each "id", and want to > take the average of the values of a particular column? I know I can > probably put something together using merge() and by() and then > munging the results together myself, but is there something in R to > perform this automatically? aggregate, by, *apply but AFAIK only after merge > > The second thing I'd like to do is like a cross-tab query; that is > when after a merge() I end up with multiple rows for a particular > "id", and want to cross-tab the data so that the multiple values > become columns and I end up with one row for each "id" again e.g. reshape in base or reShape in Hmisc is probably what you need Cheers Petr > > ID Val > 1 5 > 1 10 > 2 15 > 2 20 > > Becomes > > ID Val1 Val2 > 1 5 10 > 2 15 20 > > Thanks in advance! > > Mick > > ______________________________________________ > [EMAIL PROTECTED] mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! > http://www.R-project.org/posting-guide.html Petr Pikal [EMAIL PROTECTED] ______________________________________________ [EMAIL PROTECTED] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
