They aren’t the same though, are they? One is a copy, the other is a swap. Hence the function names. My favourite is: a = b; Where a and b are vectors.
&something gives you the address of the std::vector object, not the address of the data it holds. &something.begin() gives you the address of the iterator returned by begin() (as the compiler warns, this is not technically allowed because something.begin() is an rvalue expression, so its address cannot be taken). Assuming the container has at least … Read more
Use the partial argument of sort(). For the second highest value: n <- length(x) sort(x,partial=n-1)[n-1]
Using C++11/C++0x compile flags, you can auto it = max_element(std::begin(cloud), std::end(cloud)); // C++11 Otherwise, write your own: template <typename T, size_t N> const T* mybegin(const T (&a)[N]) { return a; } template <typename T, size_t N> const T* myend (const T (&a)[N]) { return a+N; } See it live at http://ideone.com/aDkhW: #include <iostream> #include <algorithm> … Read more
Consider whether you really need all this data explicitly, or can the matrix be sparse? There is good support in R (see Matrix package for e.g.) for sparse matrices. Keep all other processes and objects in R to a minimum when you need to make objects of this size. Use gc() to clear now unused … Read more
Appending to an object in a for loop causes the entire object to be copied on every iteration, which causes a lot of people to say “R is slow”, or “R loops should be avoided”. As BrodieG mentioned in the comments: it is much better to pre-allocate a vector of the desired length, then set … Read more
The two functions do vastly different things! The resize() method (and passing argument to constructor is equivalent to that) will insert or delete appropriate number of elements to the vector to make it given size (it has optional second argument to specify their value). It will affect the size(), iteration will go over all those … Read more
It’s called a vector because Alex Stepanov, the designer of the Standard Template Library, was looking for a name to distinguish it from built-in arrays. He admits now that he made a mistake, because mathematics already uses the term ‘vector’ for a fixed-length sequence of numbers. C++11 compounds this mistake by introducing a class ‘array’ … Read more
There might be a cleverer way to go about this, but intersect(intersect(a,b),c) will do the job. EDIT: More cleverly, and more conveniently if you have a lot of arguments: Reduce(intersect, list(a,b,c))
There’s a function std::reverse in the algorithm header for this purpose. #include <vector> #include <algorithm> int main() { std::vector<int> a; std::reverse(a.begin(), a.end()); return 0; }