Rcpp :: DataFrame :: createは20引数で制限されていますか？

Question

我々はRcpp関数内、次のデータフレームを作成している：

Rcpp::DataFrame res = 
    Rcpp::DataFrame::create(
    Rcpp::Named("A")=a 
    ,Rcpp::Named("B")=b 
    ,Rcpp::Named("C")=c 
    ,Rcpp::Named("D")=d 
    ,Rcpp::Named("E")=e 
    ,Rcpp::Named("F")=f 
    ,Rcpp::Named("G")=g 
    ,Rcpp::Named("H")=h 
    ,Rcpp::Named("I")=i 
    ,Rcpp::Named("J")=j 
    ,Rcpp::Named("K")=k 
    ,Rcpp::Named("L")=l 
    ,Rcpp::Named("M")=m 
    ,Rcpp::Named("N")=n 
    ,Rcpp::Named("O")=o 
    ,Rcpp::Named("P")=p 
    ,Rcpp::Named("Q")=q 
    ,Rcpp::Named("R")=r 
    ,Rcpp::Named("S")=s 
    ,Rcpp::Named("T")=t 
    ,Rcpp::Named("U")=u 
); 

このデータフレームは、返された結果として意図されています。ただし、次のエラーのためコンパイルできません。

error: no matching function for call to Rcpp::DataFrame_Impl<Rcpp::PreserveStorage>::create 
In file included from local/lib64/R/library/Rcpp/include/Rcpp/DataFrame.h:97:0, 
       from local/lib64/R/library/Rcpp/include/Rcpp.h:57, 
       from file54f121e6a937.cpp:1: 
local/lib64/R/library/Rcpp/include/Rcpp/generated/DataFrame_generated.h:142:23: note: template<class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15, class T16, class T17, class T18, class T19, class T20> static Rcpp::DataFrame_Impl<StoragePolicy> Rcpp::DataFrame_Impl<StoragePolicy>::create(const T1&, const T2&, const T3&, const T4&, const T5&, const T6&, const T7&, const T8&, const T9&, const T10&, const T11&, const T12&, const T13&, const T14&, const T15&, const T16&, const T17&, const T18&, const T19&, const T20&) [with T1 = T1; T2 = T2; T3 = T3; T4 = T4; T5 = T5; T6 = T6; T7 = T7; T8 = T8; T9 = T9; T10 = T10; T11 = T11; T12 = T12; T13 = T13; T14 = T14; T15 = T15; T16 = T16; T17 = T17; T18 = T18; T19 = T19; T20 = T20; StoragePolicy = Rcpp::PreserveStorage] 
static DataFrame_Impl create(const T1& t1, const T2& t2, const T3& t3, const T4& t4, const T5& t5, const T6& t6, const T7& t7, const T8& t8, const T9& t9, const T10& t10, const T11& t11, const T12& t12, const T13& t13, const T14& t14, const T15& t15, const T16& t16, const T17& t17, const T18& t18, const T19& t19, const T20& t20) { 
        ^
local/lib64/R/library/Rcpp/include/Rcpp/generated/DataFrame_generated.h:142:23: note: template argument deduction/substitution failed: 
file54f121e6a937.cpp:771:7: note: candidate expects 20 arguments, 21 provided 

20の引数で正常に動作します。どのようにこの問題を克服するのですか？おかげで

Answer 1

はい。これは、私の頭の上オフ

...さまざまな場所でカバーされています

https://cran.r-project.org/web/packages/Rcpp/vignettes/Rcpp-FAQ.pdf#page=17

In essence, and in order to be able to compile it with the largest number of compilers, Rcpp is constrained by the older C++ standards which do not support variadic function arguments. So we actually use macros and code generator scripts to explicitly enumerate arguments, and that number has to stop at some limit. We chose 20.

---

アプローチは、20の以上の列を持つdata.frameを作成するために使用することですlistを作成し、次にdata.frameに強制します。

サンプルコード：

#include <Rcpp.h> 

// [[Rcpp::export]] 
Rcpp::List dynamic_df(Rcpp::DataFrame df) { 

    // Number of variables in data.frame 
    int num_vars = df.ncol(); 

    // Instantiate list with p variable entries 
    Rcpp::List long_list(num_vars); 

    // Make a variable to name columns 
    Rcpp::CharacterVector namevec(num_vars); 

    // Copy from data.frame into list. 
    for (int i=0;i < num_vars; ++i) { 
    long_list[i] = df(i); // Move vector from data frame to list 
    namevec[i] = i; 
    } 

    // Add colnames 
    long_list.attr("names") = namevec; 

    // Coerce list to data.frame 
    long_list.attr("row.names") = Rcpp::IntegerVector::create(NA_INTEGER, df.nrow()); 
    long_list.attr("class") = "data.frame"; 

    // Return result.. Will appear as data.frame 
    return long_list; 
} 

/*** R 

head(dynamic_df(mtcars)) 

*/ 

出力：

head(dynamic_df(mtcars)) 
#  0 1 2 3 4  5  6 7 8 9 10 
# 1 21.0 6 160 110 3.90 2.620 16.46 0 1 4 4 
# 2 21.0 6 160 110 3.90 2.875 17.02 0 1 4 4 
# 3 22.8 4 108 93 3.85 2.320 18.61 1 1 4 1 
# 4 21.4 6 258 110 3.08 3.215 19.44 1 0 3 1 
# 5 18.7 8 360 175 3.15 3.440 17.02 0 0 3 2 
# 6 18.1 6 225 105 2.76 3.460 20.22 1 0 3 1 

---

けれども、あなたが本当に重複したエントリにケビンによるList_Builderクラスを使用して検討すべきです。

c.f.

how many vectors can be added in DataFrame::create(vec1, vec2 ...)?