默认NULL参数Rcpp [英] Default NULL parameter Rcpp
问题描述
我试图用Rcpp
中的默认NULL
参数定义一个函数.以下是一个示例:
I am trying to define a function with a default NULL
parameter in Rcpp
. Following is an example:
// [[Rcpp::export]]
int test(int a, IntegerVector kfolds = R_NilValue)
{
if (Rf_isNull(kfolds))
{
cout << "NULL" << endl;
}
else
{
cout << "NOT NULL" << endl;
}
return a;
}
但是当我运行代码时:
test(1)
我收到以下错误:
错误:与请求的类型不兼容
Error: not compatible with requested type
我该如何解决这个问题?
How can I solve this issue?
推荐答案
您很幸运.我们在 mvabund 和 Rblpapi ,并且自上一(两个)Rcpp版本发布以来就拥有它.
You are in luck. We needed this in mvabund and Rblpapi, and have it since the last (two) Rcpp releases.
所以尝试一下:
// [[Rcpp::export]]
int test(int a, Rcpp::Nullable<Rcpp::IntegerVector> kfolds = R_NilValue) {
if (kfolds.isNotNull()) {
// ... your code here but note inverted test ...
一个很好的完整示例是在Rblpapi中. 您还可以像以前一样设置默认值(要遵循C ++中所有选项右侧的所有选项的常规规则,该选项也具有默认值).
A nice complete example is here in Rblpapi. You can also set a default value as you did (subject to the usual rules in C++ of all options to the right of this one also having defaults).
为完整起见,这是一个完整的示例:
For completeness sake, here is a full example:
#include <Rcpp.h>
// [[Rcpp::export]]
int testfun(Rcpp::Nullable<Rcpp::IntegerVector> kfolds = R_NilValue) {
if (kfolds.isNotNull()) {
Rcpp::IntegerVector x(kfolds);
Rcpp::Rcout << "Not NULL\n";
Rcpp::Rcout << x << std::endl;
} else {
Rcpp::Rcout << "Is NULL\n";
}
return(42);
}
/*** R
testfun(NULL)
testfun(c(1L, 3L, 5L))
*/
生成以下输出:
R> sourceCpp("/tmp/nick.cpp")
R> sourceCpp("/tmp/nick.cpp")
R> testfun(NULL)
Is NULL
[1] 42
R> testfun(c(1L, 3L, 5L))
Not NULL
1 3 5
[1] 42
R>
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