Check here
<https://github.com/RevolutionAnalytics/rmr2/blob/master/pkg/src/t-list.cpp>
for something similar to Tim's solution that preallocates all vectors to
avoid the costly push_back. Still needs the unlists in R, so it's expensive
in that dimension, the number of lists in the output.
Antonio
On Sun, May 3, 2015 at 4:22 PM, Tim Keitt <tke...@utexas.edu> wrote:
> A slightly improved version:
>
> library(Rcpp)
>
> code = '
> SEXP test(List a)
> {
> auto l = Rf_length(a[0]);
> using svec = std::vector<SEXP>;
> std::vector<svec> x(l);
> for (List b : a)
> {
> if (b.size() != l)
> stop("Ragged input");
> for (int i = 0; i != l; ++i)
> x[i].push_back(b[i]);
> }
> return wrap(x);
> }'
>
> f = cppFunction(code = code, plugins = "cpp11")
>
> res = lapply(f(list(list(T, 1, 'a'),
> list(F, 2, 'b'))),
> unlist)
>
>
> On Sun, May 3, 2015 at 11:57 AM, Tim Keitt <tke...@utexas.edu> wrote:
>
>> Here's a really bare-bones version. Not very pretty or complete, but it
>> does do the job. Could the 'unlist' part be converted to Rcpp?
>>
>> THK
>>
>> library(Rcpp)
>>
>> code = '
>> SEXP test(List a)
>> {
>> int l = Rf_length(a[0]);
>> typedef std::vector<SEXP> svec;
>> std::vector<svec> x(l);
>> for (int i = 0; i != l; ++i)
>> for (int j = 0; j != a.size(); ++j)
>> {
>> List b = a[j];
>> x[i].push_back(b[i]);
>> }
>> return wrap(x);
>> }'
>>
>> f = cppFunction(code = code)
>>
>> res = lapply(f(list(list(1, 'a'), list(2, 'b'))), unlist)
>>
>>
>> On Sat, May 2, 2015 at 1:18 PM, Dirk Eddelbuettel <e...@debian.org> wrote:
>>
>>>
>>> On 2 May 2015 at 10:49, William Dunlap wrote:
>>> | Since translation from R to Rcpp is "seamless" I will leave that to
>>> you.
>>>
>>> One problem is with the strongly typed nature of C++. Rearranging
>>> dynamicly
>>> growing objects can be done. I think I used Boost's variant type a few
>>> years. I am sure there are other possibilities. We should collect a
>>> few and
>>> compare. But in C++ please :)
>>>
>>> Dirk
>>>
>>> --
>>> http://dirk.eddelbuettel.com | @eddelbuettel | e...@debian.org
>>>
>>
>>
>>
>> --
>> http://www.keittlab.org/
>>
>
>
>
> --
> http://www.keittlab.org/
>
> _______________________________________________
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