Rcpp错误:从'Rcpp::Vector<13，Rcpp::PreserveStorage>‘类型到'int’类型的无效Rcpp：：PreserveStorage>

Question

我目前正在为类分配(“解决”背包问题)编写模拟退火算法，并希望在Rcpp中进行(我必须使用R，而且Rcpp更快)。

Rcpp给了我以下错误

invalid static_cast from type 'Rcpp::Vector<13, Rcpp::PreserveStorage>' to type 'int'

这指的是Rcpp内部caster.h的第30行

在过去的几个小时里，我一直在谷歌搜索，但没有结果，我也不知道问题出在哪里。有人有什么想法吗？谢谢。

#include <RcppArmadilloExtensions/sample.h>
#include <Rcpp.h>
// [[Rcpp::depends(RcppArmadillo)]]
using namespace Rcpp;

// [[Rcpp::export]]
List ska(NumericVector objWeight,
         NumericVector objValue,
         float maxWeight, 
         float tau,
         int N) {
  // m .... weight of objects
  // V .... value of objects
  // M .... maximum weight allowed
  // tau .. starting temperature
  // N .... number of iterations

  RNGScope scope;

  int nObj;
  IntegerVector Obj;

  nObj = objWeight.length();
  Obj = seq_len(nObj);

  IntegerVector curObj = IntegerVector::create(1);
  float curValue;
  float curWeight;

  NumericVector tempVector;
  IntegerVector tempIn;
  IntegerVector tempOut;
  float tempSum;

  tempVector = objValue[curObj];
  curValue = std::accumulate(tempVector.begin(), tempVector.end(), 0.0);

  tempVector = objWeight[curObj];
  curWeight = std::accumulate(tempVector.begin(), tempVector.end(), 0.0);

  IntegerVector bestObj;
  float bestValue;
  float bestWeight;

  bestObj = curObj;
  bestValue = curValue;
  bestWeight = curWeight;

  IntegerVector tempObj;
  float tempValue;
  float tempWeight;

  float testLHS;
  float testRHS;

  LogicalVector subsetOther;
  LogicalVector subsetTemp;

  IntegerVector otherObj;

  for (int i = 0; i < N; i++) {
    tempObj = curObj;

    tempVector = objWeight[tempObj - 1];
    tempSum = std::accumulate(tempVector.begin(), tempVector.end(), 0.0);

    while (tempSum <= maxWeight) {
      // adding random objects until over maxWeight
      subsetOther = !in(tempObj, Obj);
      otherObj = Obj[subsetOther];

      tempIn = RcppArmadillo::sample(otherObj, 1, false);
      tempObj.push_back(tempIn);

      tempVector = objWeight[tempObj - 1];
      tempSum = std::accumulate(tempVector.begin(), tempVector.end(), 0.0);
    }

    while (tempSum > maxWeight) {
      // removing random objects until under maxWeight
      tempOut = RcppArmadillo::sample(tempObj, 1, false);

      subsetTemp = !in(tempOut, tempObj);
      tempObj = tempObj[subsetTemp];

      tempVector = objWeight[tempObj - 1];
      tempSum = std::accumulate(tempVector.begin(), tempVector.end(), 0.0);
    }

    // calculate the values for this iteration
    tempWeight = tempSum;

    tempVector = objValue[tempObj - 1];
    tempValue = std::accumulate(tempVector.begin(), tempVector.end(), 0.0);

    if (tempValue > bestValue) {
      bestObj = tempObj;
      bestValue = tempValue;
      bestWeight = tempWeight;
    }

    // candidate acceptance
    testLHS = R::runif(0,1);
    testRHS = exp((curValue - tempValue) / (tau / i));

    if(testLHS < testRHS) {
      curObj = tempObj;
      curValue = tempValue;
    }
  }

  return List::create(_["Objects"] = bestObj,
                      _["Total_value"] = bestValue,
                      _["Total_weight"] = bestWeight);
}

编译器错误：

D:/R/library/Rcpp/include/Rcpp/internal/caster.h: In function 'TO Rcpp::internal::caster(FROM) [with FROM = Rcpp::Vector<13, Rcpp::PreserveStorage>, TO = int]':
D:/R/library/Rcpp/include/Rcpp/vector/converter.h:34:33:   instantiated from 'static Rcpp::internal::element_converter<RTYPE>::target Rcpp::internal::element_converter<RTYPE>::get(const T&) [with T = Rcpp::Vector<13, Rcpp::PreserveStorage>, int RTYPE = 13, Rcpp::internal::element_converter<RTYPE>::target = int]'
D:/R/library/Rcpp/include/Rcpp/vector/Vector.h:426:9:   instantiated from 'void Rcpp::Vector<RTYPE, StoragePolicy>::push_back(const T&) [with T = Rcpp::Vector<13, Rcpp::PreserveStorage>, int RTYPE = 13, StoragePolicy = Rcpp::PreserveStorage]'
ska.cpp:73:31:   instantiated from here
D:/R/library/Rcpp/include/Rcpp/internal/caster.h:30:29: error: invalid static_cast from type 'Rcpp::Vector<13, Rcpp::PreserveStorage>' to type 'int'
D:/R/library/Rcpp/include/Rcpp/internal/caster.h:31:1: warning: control reaches end of non-void function [-Wreturn-type]
make: *** [ska.o] Error 1
Warning message:
running command 'make -f "D:/R/etc/x64/Makeconf" -f "D:/R/share/make/winshlib.mk" SHLIB_LDFLAGS='$(SHLIB_CXXLDFLAGS)' SHLIB_LD='$(SHLIB_CXXLD)' SHLIB="sourceCpp_61.dll" WIN=64 TCLBIN=64 OBJECTS="ska.o"' had status 2 

Answer 1

就是这些任务：

tempVector = objValue[curObj];
tempVector = objWeight[curObj];
...

objWeight和objValue是NumericVector，您要将任何NumericVector::operator[]返回给另一个NumericVector。我想这不是一个NumericVector，而是一个元素，这就是为什么您的代码不编译。

我不知道Rcpp，但我确信您希望执行其他操作(比如追加元素？)。