On May 9, 2013, at 7:06 PM, jpm miao wrote: > Hi, > > As an example, how can I get the data such that field a of ab, ab["a"], > equals 3? I expect the answer to be the union of 2 and 4, as > > Thanks, > >> a<-c(1,3,4,3,5,6,5) >> b<-c(2,4,6,7,3,1,2) >> ab<-data.frame(a,b) >> ab > a b > 1 1 2 > 2 3 4 > 3 4 6 > 4 3 7 > 5 5 3 > 6 6 1 > 7 5 2 > >> ab[a==3] > Error in `[.data.frame`(ab, a == 3) : undefined columns selected >> ab[ab["a"]==3] > [1] 3 3 4 7 > Try;
ab[ ab[["a"]]==3, ] And then read ?Extract to help drive home the point the ab["a"] is a list with one element and ab[["a"]] is a vector with 7 elements. -- David Winsemius Alameda, CA, USA ______________________________________________ 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.
