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. :-) 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| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ [[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.
