Inline below On Sun, Dec 4, 2011 at 10:29 AM, Costas Vorlow <costas.vor...@gmail.com> wrote: > Dear Bert, > > You are right (obviously). > > Apologies for any inconvenience caused. I thought my problem was simplistic > with a very obvious answer which eluded me. > > As per your justified questions : > > 2: Answer is "all", > > hence: > > 3. would be include overlapping set (I guess) but this does not matter for > the time being. I didn't give it too much thought admittedly... If I got 1 & > 2 right I could have modified the code for point 3 (if answer in 2 != > "all'), so I did not consider it when I was formulating my query. However, I > can see now why this is confusing. > > Anyways, thanks again for the pointers. > > BTW, is there a good & quick read/guide on vectorization in R that one could > recommend? That would minimize my queries at least in the list. :-)
Vectorization is a central paradigm in R, so practically all books on the S language discuss this. The "R language definition" manual that ships with R is pretty comprehensive, but V&R's MASS or S Programming Books, Patrick Burns's website tutorials (he has several well suited for beginners), John Chambers's "Programming with R " , etc. are just a few among many. It is impossible for me to be more specific than that. -- Bert > > Apologies again and best regards, > Costas > > On 4 December 2011 17:45, Bert Gunter <gunter.ber...@gene.com> wrote: >> >> Costas: (and thanks for giving us your name) >> >> which(x == 1) >> >> gives you the indices where x is 1 (up to floating point equality -- >> you did not specify whether your x values are integers or calculated >> as floating point, and that certainly makes a difference). You can >> then use simple indexing to get the y values. No loops needed. >> >> However, let's explore why your question may have been too poorly >> formed to get the answer you seek: >> >> 1. What if the index of the first 1 is 3 or less? -- Do you want to >> ignore the (less than 3) preceding values or just choose as many as >> you can? >> >> 2. What if, as in your example, several 1's occur in x. Do you want >> the 3 preceding values for all of them or just the first? >> >> 3. If the answer to 2 is "all of them," what if several 1's are less >> than 3 indices apart -- do you want to include the overlapping sets of >> 3 y's -- or what? >> >> My point is that "etc. etc." is simply inadequate as a coherent or >> useful problem description in your post. You _must_ be explicit, >> complete, and concise. This can be hard. Indeed, it may require >> considerable thought and effort. I have found -- and others have often >> noted here -- that going through such an exercise itself often reveals >> a solution. But be that as it may, the Posting Guide is actually an >> excellent, comprehensive discussion of how to ask good questions in >> forums like this. Read it. Follow it. >> >> ... and to be fair, your post below is, imho, probably above average >> as posts go, allowing me to focus on specific points that I thought >> required clarification. Quite a few posts here of late have been so >> muddled and incoherent that I had no clue what the OP wanted. And it's >> not English as a second language. I am a language ignoramus and speak >> only English, so I am happy to tolerate poor grammar and vocabulary >> from someone for whom English is only one of several languages in >> which they can communicate. The problem is poor thinking, not poor >> English. >> >> Best, >> Bert >> >> On Sun, Dec 4, 2011 at 7:18 AM, Costas Vorlow <costas.vor...@gmail.com> >> wrote: >> > Hello, >> > >> > I am having problems vectorizing the following (i/o using a >> > for/next/while >> > loop): >> > >> > I have 2 sequences such as: >> > >> > x, y >> > 1, 30 >> > 2, -40 >> > 0, 50 >> > 0, 25 >> > 1, -5 >> > 2, -10 >> > 1, 5 >> > 0, 40 >> > >> > etc etc >> > >> > The first sequence (x) takes integer numbers only: 0, 1, 2 >> > The sequence y can be anything... >> > >> > I want to be able to retrieve (in a list if possible) the 3 last values >> > of >> > the y sequence before a value of 1 is encountered on the x sequence, >> > i.e: >> > >> > On line 5 in the above dataset, x is 1 so I need to capture values: 25, >> > 50 >> > and -40 of the y sequence. >> > >> > So the outcome (if a list) should look something like: >> > >> > [1],[25,50,-40] >> > [2],[-10,-5,25] # as member #7 of x sequence is 1... >> > >> > etc. etc. >> > >> > Can I do the above avoiding for/next or while loops? >> > I am not sure I can explain it better. Any help/pointer extremely >> > welcome. >> > >> > Best regards, >> > Costas >> > >> > >> > -- >> > >> > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ >> > |c|o|s|t|a|s|@|v|o|r|l|o|w|.|o|r|g| >> > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ >> > >> > [[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. >> >> >> >> -- >> >> Bert Gunter >> Genentech Nonclinical Biostatistics >> >> Internal Contact Info: >> Phone: 467-7374 >> Website: >> >> http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm > > > > > -- > > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > |c|o|s|t|a|s|@|v|o|r|l|o|w|.|o|r|g| > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > -- Bert Gunter Genentech Nonclinical Biostatistics Internal Contact Info: Phone: 467-7374 Website: http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm ______________________________________________ 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.
