For loops are not slow. Inefficient memory management in for loops is slow. Feel free to preallocate your output vectors and write for loops to your heart's content. If you really want speed you can write this in C++ using Rcpp [1]. If your f() is a standard digital filter algorithm this has already been done for you (see ?filter).
[1] https://stat.ethz.ch/pipermail/r-help//2014-December/424027.html --------------------------------------------------------------------------- Jeff Newmiller The ..... ..... Go Live... DCN:<jdnew...@dcn.davis.ca.us> Basics: ##.#. ##.#. Live Go... Live: OO#.. Dead: OO#.. Playing Research Engineer (Solar/Batteries O.O#. #.O#. with /Software/Embedded Controllers) .OO#. .OO#. rocks...1k --------------------------------------------------------------------------- Sent from my phone. Please excuse my brevity. On May 27, 2015 4:34:01 PM PDT, blue honour via R-help <r-help@r-project.org> wrote: >Hi all, > >Let's say I have a vector: > >vv<-c(1,2,3) > > >And suppose I have a function f(a,b), which is a function of 2 scalar >inputs. I would like to evaluate this function separately for each >element of the vv vector while the second input to f( ) will be the >previous output from f( ). So, the valuation of f() has a dependency on >the previous f( ) valuation (recursive). This type of calculation is >easy to set up with a for loop but that will run slow. How can I >achieve this with apply family of functions please? > >I have the same question for the case when vv is a data.table instead >of a vector. > >Thank you for any help. > >______________________________________________ >R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see >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. ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.
