hi Jorge, > * Jorge I Velez <wbetrvinair...@tznvy.pbz> [2012-10-18 16:43:58 +1100]: > >> a <- factor(5:1,levels=1:9) >> b <- factor(9:1,levels=1:9) >> lev <- sort(unique(f <- c(a, b))) >> f <- factor(f, levels = lev) >> str(f) > Factor w/ 9 levels "1","2","3","4",..: 5 4 3 2 1 9 8 7 6 5 ...
is sort(unique()) really necessary? I think lev <- levels(a) should be enough. However, this does not quite do what I want. I want a function which will _NOT_ have a non-factor vector as an intermediate value because that would waste a LOT of memory in my case. I want a function which will check that a and b have identical levels (in Lisp lingo, the levels are EQ, not just EQUALP). --8<---------------cut here---------------start------------->8--- > a <- factor(letters[sample(1:10,20,replace=TRUE)],levels=letters) [1] e e a b c e j d a b h i a e e g j a c e Levels: a b c d e f g h i j k l m n o p q r s t u v w x y z > b <- factor(letters[sample(1:10,30,replace=TRUE)],levels=letters) [1] d d f c j b d e j j g i g j j g g a j a b e d c b i i a b f Levels: a b c d e f g h i j k l m n o p q r s t u v w x y z > c(a,b) [1] 5 5 1 2 3 5 10 4 1 2 8 9 1 5 5 7 10 1 3 5 4 4 6 3 10 [26] 2 4 5 10 10 7 9 7 10 10 7 7 1 10 1 2 5 4 3 2 9 9 1 2 6 > factor(letters[c(a,b)],levels=letters) [1] e e a b c e j d a b h i a e e g j a c e d d f c j b d e j j g i g j j g g a [39] j a b e d c b i i a b f Levels: a b c d e f g h i j k l m n o p q r s t u v w x y z --8<---------------cut here---------------end--------------->8--- however, this is not a "direct" way (unlike my unlist(list(...))): there is an intermediate integer vector c(a,b) which is mapped to a character vector via letters, which is converted back to integers (==factors). IIUC, a factor is an integer vector which knows that the integers refer to levels. c(a,b) creates such an integer vector. How do I tell it that it is a factor? -- Sam Steingold (http://sds.podval.org/) on Ubuntu 12.04 (precise) X 11.0.11103000 http://www.childpsy.net/ http://palestinefacts.org http://www.memritv.org http://www.PetitionOnline.com/tap12009/ http://dhimmi.com usually: can't pay ==> don't buy. software: can't buy ==> don't pay ______________________________________________ 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.
