Hello Dirk and others, Dirk - Thank you for the quick reply!
Some responses: 1) I looked at the Rcpp gallery. The best I found was: http://gallery.rcpp.org/articles/setting-object-attributes/ (which already was available in Hadley's book) And: http://gallery.rcpp.org/articles/modifying-a-data-frame/ http://gallery.rcpp.org/articles/reversing-a-vector/ And also now at unitTests/cpp/DataFrame (interesting) But none have helped me with getting the attributes of an element inside a List. That is, say that we have x as a List, how do we go about fetching its attr? I tried: x[1].attr("type") x.attr[1]("type") But none seemed to have worked. Any suggestions there? 2) Your book is on my "to get a hold of somehow" list. Getting books to Israel is always trickier - I might just get it when I'll visit the US in a few months. 3) The post on Rcpp didn't get on R-bloggers since it wasn't marked with the "R" category. http://blog.revolutionanalytics.com/2013/07/deepen-your-r-experience-with-rcpp.html (David could still fix it if he wants to - and set the date of the post to be more recent) 4) Having an is<List>(x) will be nice. Although I will need to see some examples to see when it is better then simply using: x.inherits("list") 5) I couldn't find a 'dispatch on type' example in the Rcpp gallery. I'm probably missing something in how I'm searching there. 6) Environment.cpp in the unitTest is interesting. It is probably what I needed. 7) To Dirk and others - I will be happy to wait a bit to see if any of you can help by writing the R functions from my previous e-mail in Rcpp. That would be a big help for me in understanding how the relevant pieces should fit together. (the functions themselves are not useful, but they require many of the features I imagine I will need later on). Cheers, Tal ----------------Contact Details:------------------------------------------------------- Contact me: tal.gal...@gmail.com | Read me: www.talgalili.com (Hebrew) | www.biostatistics.co.il (Hebrew) | www.r-statistics.com (English) ---------------------------------------------------------------------------------------------- On Sat, Jul 20, 2013 at 8:47 PM, Dirk Eddelbuettel <e...@debian.org> wrote: > > Hi Tal, > > And welcome! > > On 20 July 2013 at 19:44, Tal Galili wrote: > | Hello dear Rcpp users, > | > | First - I'd like to say that I took Hadley and Romain's workshop at the > useR > | conference this year, and I am very excited about trying out Rcpp - this > | project looks AMAZING. > > Your feedback (as conveyed earlier in private email) is much appreciated. > > There was a second, and also very positive, response to the same workshop: > Joe posted it on the REvo blog last week---somehow that never made it > through > R Bloggers, I think. > > | Second - this is my first post, and I apologize if my question is too > basic. To > | my defense, I tried looking through this mailing list / googled before > asking, > | and read through Hadley's github chapter on Rcpp. > > I hear there is a book on Rcpp too :) > > | The questions: > | > | I am looking to understand better how List objects can be navigated, > their > | elements accessed, and manipulated - using Rcpp. > | > | For example, here is an R list object: > | > | x <- list(a = 1, b = 2, c = list(ca = 3, cb = 4, 5), 6) > | attr(x[[1]], "type") = "fun" > | attr(x[[3]][[1]], "type") = "fun" > | x > | > | I would like to create two types of functions: > | 1) A function that will go through "x" and will RETURN all of the > elements > | within it that are of type "fun". > | In R I would do it like this: > | > | return_fun <- function(x) { > | fun_nubmers <- numeric() > | for(i in seq_along(x)) { > | if(class(x[[i]]) == "list") { > | fun_nubmers <- c(fun_nubmers, return_fun(x[[i]])) > | } else { > | if(!is.null(attr(x[[i]], "type"))) { > | if(attr(x[[i]], "type") == "fun") fun_nubmers <- > c(fun_nubmers, x > | [[i]]) > | } > | } > | } > | return fun_nubmers > | } > | return_fun(x) # output: 1 3 > | > | But in Rcpp there are many parts to this R function that I don't know > how to > | do. I don't know how to access the attributes of a sub-element within a > List, I > | don't know how to check if that attribute is null or not, etc. So any > | suggestions on either reading material (or better yet - an example of > how this > | function might be created in Rcpp would be great. > > You can access attributes, pretty much as in R. You can access lists > within > lists, pretty much as in R. > > Two quick pointers to working examples: > > -- our unit tests, especially now that they all have been rewritten via > Rcpp attributes to be R files calling sourceCpp on C++ files: > > edd@max:~$ grep -l attr > /usr/local/lib/R/site-library/Rcpp/unitTests/cpp/* > /usr/local/lib/R/site-library/Rcpp/unitTests/cpp/DataFrame.cpp > /usr/local/lib/R/site-library/Rcpp/unitTests/cpp/S4.cpp > edd@max:~$ > > -- the Rcpp Gallery which has several posts on attr > > Likewise, Lists within lists can be accessed as well. You need to test each > element for its type. The Rcpp Gallery has a 'dispatch on type' example as > I > recall. These still use the C API of R --- but Romain just added beginnings > of is<foo>(x) tests to Rcpp's SVN which will help with tasks like this. > > | 2) A function that will go through "x" and will CHANGE all of the > elements > | within it that are of type "fun". For example, adding 1 to them. > | In R I would do it like this: > | > | add1_fun <- function(x) { > | for(i in seq_along(x)) { > | if(class(x[[i]]) == "list") { > | x[[i]] <- add1_fun(x[[i]]) > | } else { > | if(!is.null(attr(x[[i]], "type"))) { > | if(attr(x[[i]], "type") == "fun") x[[i]] <- x[[i]] + 1 > | } > | } > | } > | x > | } > | add1_fun(x) > | return_fun(x) # output: 1 3 > | return_fun(add1_fun(x) ) # output: 2 4 > > That is similar -- you need to test and recurse as well. > > | 3) Is it possible to work with some "global" variable from within a > recursive > | Rcpp function? > | For example: > | > | > | count_till_5 <- function() { > | if(!exists("global_var")) global_var = 0 > | > | if(global_var <5) { > | global_var <<- global_var+1 > | count_till_5() > | } > | } > | count_till_5() > | global_var > | > | Is there a way to create something like this with Rcpp? > > Yes by using the Environment class and accessing elements from a given > environment -- here the global one. > > Again, I think the Rcpp Gallery has a Environment example. The unit tests > do. > > These are all nice yet not entirely trivial questions. I would like try to > cook something up (unless somebody beats me to it) but I have a things I > need > to be working on instead ... > > Cheers, Dirk > > -- > Dirk Eddelbuettel | e...@debian.org | http://dirk.eddelbuettel.com >
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