First, some general suggestions: To see the structure of an object I would recommend the str() function or, for a more concise output, the class() function.
I don't think most ordinary users should be using is.list() and, especially, is.vector(). Now for the particulars. dbGetQuery probably returns an object of class "data.frame". data.frames are implemented as lists with certain attributes, so if 'dat' is a data.frame then is.list(dat) reports TRUE. class(dat) would report "data.frame", which is what you want to know. Similarly, dat[1] is a data.frame so is.list(dat[1]) reports TRUE. dat[[1]] is a column of a data.frame, not a data.frame, and class(dat[[1]]) will tell you its class. I haven't come across a case where is.vector is useful. is.vector(x) returns TRUE if x has no attributes other than "names" is x is not a language object, environment, or other esoteric type. E.g., is.vector of a factor object returns FALSE and is.vector of a numeric object or a list object returns TRUE (unless the object has some attributes). is.vector has nothing to do with the concept of a vector in linear algebra (or aviation or physics or almost anywhere else). Bill Dunlap Spotfire, TIBCO Software wdunlap tibco.com > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On > Behalf Of Kehl Dániel > Sent: Monday, December 05, 2011 11:21 AM > To: r-help@r-project.org > Subject: [R] lists everywhere > > Dear list members, > > I have a really simple problem. > I connected to a DB and have the following query > > adat <- dbGetQuery(con, paste("select * from kmdata where SzeAZ='", > szeazok[i], "' order by datum", sep="")) > > now I have the data in the adat variable which is a list. In fact the > elements of the list are lists as well > > is.list(adat) > [1] TRUE > > is.list(adat[10]) > [1] TRUE > > is.list(adat[[10]]) > [1] FALSE > > is.vector(adat[[10]]) > [1] TRUE > > I simply want to use a function with sapply on the 13-76th columns of > the original list. > sapply(data[[13:76]], myfunc) does not work of course. I tried to define > 13:76 in a vector, still no result. > How is it possible? > > thanks a lot > d > > ______________________________________________ > 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. ______________________________________________ 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.
