C++ tricks

trickCpp.cpp

#include <algorithm>
#include <iostream>
#include <vector>
 
// quickly find the position of the minimum and maximum elements of an STL vector
int main()
{
    std::vector<int> v = { 3, 9, 1, 4, 2, 5, 9 };
 
    auto result = std::minmax_element(v.begin(), v.end());
    std::cout << "min element at: " << (result.first - v.begin()) << '\n';
    std::cout << "max element at: " << (result.second - v.begin()) << '\n';
}

// find the min and max seperately, but getting slightly more information.
#include <algorithm>
#include <iostream>
#include <vector>

int main()
{
    std::vector<double> v {1.0, 2.0, 3.0, 4.0, 5.0, 1.0, 2.0, 3.0, 4.0, 5.0};

    auto biggest = std::max_element(std::begin(v), std::end(v));
    std::cout << "Max element is " << *biggest
        << " at position " << std::distance(std::begin(v), biggest) << std::endl;

    auto smallest = std::min_element(std::begin(v), std::end(v));
    std::cout << "min element is " << *smallest
        << " at position " << std::distance(std::begin(v), smallest) << std::endl;
}

// fake '...' argument in Rcpp
void testEllipses(Function fun, double x, List ellipses){
 double out = as<double>(fun(x,ellipses));
 Rcout << out << std::endl;
}

// take one thing out of a vector quickly
int main()
{
    std::vector<int> v = { 3, 9, 1, 4, 2, 5, 9 };
    
    for (auto i = v.begin(); i != v.end(); ++i){
        std::cout << *i << ' ';
    }
    std::cout << "" << std::endl;
 
    v[1] = v.back(); // remove 2nd element from vector
    v.pop_back();
    
    for (auto i = v.begin(); i != v.end(); ++i){
        std::cout << *i << ' ';
    }
}



// find stuff
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

int main()
{

 std::vector<double> v;
 v.push_back(1);
 v.push_back(1);
 v.push_back(10);
 v.push_back(1);
 v.push_back(1);
 v.push_back(10);
 v.push_back(1);
 v.push_back(7);
 v.push_back(1);
  std::vector<int> results;

auto it = std::find_if(std::begin(v), std::end(v), [](int i){return i > 5;});
while (it != std::end(v)) {
   results.emplace_back(std::distance(std::begin(v), it));
   it = std::find_if(std::next(it), std::end(v), [](int i){return i > 5;});

for(auto it = results.begin(); it != results.end(); it++){
    std::cout << "it: " << *it << std::endl;
    }

}
}




    // testing subsets of vectors
    std::vector<std::string> stringVector;
    stringVector.push_back("A");
    stringVector.push_back("B");
    stringVector.push_back("C");
    stringVector.push_back("D");
    stringVector.push_back("E");
    for(auto it = stringVector.begin(); it != stringVector.end(); it++){
        std::cout << "it: " << *it << std::endl;
    }
    
    std::vector<int> SelectionV;
    SelectionV.push_back(0);
    SelectionV.push_back(2);
    for(auto it = SelectionV.begin(); it != SelectionV.end(); it++){
        std::cout << "it: " << *it << std::endl;
    }
    
    std::vector<std::string> Result;
    Result.reserve(SelectionV.size()+10);
    
    std::transform(SelectionV.begin(), SelectionV.end(), std::back_inserter(Result), [stringVector](size_t pos) {
        return(stringVector.at(pos));
    });
    
    std::cout << "start!" << Result.size() << std::endl;
    for(auto it = Result.begin(); it != Result.end(); it++){
        std::cout << "it: " << *it << std::endl;
    }