Yes people, even though I'm talking about the R Project for Statistical Computing, it can still require programming! Suppose I have a vector that is nested in a dataframe one or two levels. Is there a quick and dirty way to access the last value, without using the length() function? Something ala PERL's $# special var? So I would lik...
I am wrapping a native C++ class, which has the following methods: class Native { public: class Local { std::string m_Str; int m_Int; }; typedef std::vector<Local> LocalVec; typedef LocalVec::iterator LocalIter; LocalIter BeginLocals(); LocalIter EndLocals(); private: LocalV...
I need a very fast algorithm for the following task. I have already implemented several algorithms that complete it, but they're all too slow for the performance I need. It should be fast enough that the algorithm can be run at least 100,000 times a second on a modern CPU. It will be implemented in C++. I am working with spans/ranges, a...
I'm writing an inner loop that needs to place structs in contiguous storage. I don't know how many of these structs there will be ahead of time. My problem is that STL's vector initializes its values to 0, so no matter what I do, I incur the cost of the initialization plus the cost of setting the struct's members to their values. Is t...
Hi, Consider these classes, class Base { ... }; class Derived : public Base { ... }; this function void BaseFoo( std::vector<Base*>vec ) { ... } And finally my vector std::vector<Derived*>derived; I want to pass derived to function BaseFoo, but the compiler doesn't let me. How do I solve this, without copying the whole vector...
When iterating over elements of a vector it is preferred to use iterators instead of an index (see Why use iterators instead of array indices?). std::vector<T> vec; std::vector<T>::iterator it; for ( it = vec.begin(); it != vec.end(); ++it ) { // do work } However, it can be necessary to use the index in the body of the loop. Whic...
Hello, I have this code inside a class: void SendStones() { int currenthole = hole; int lastplace = 0; for(int i=0;i<stns.size();i++) { while(1) {//Calculate new currenthole if(currenthole == 13) { currenthole = 7; break;} if(currenthole == 14) { currenthole = 6; break;} ...
Given a point such as (0, 0, 0) and a vector like (x, y, z). What is the easiest way to align the negative Z-axis centered at (0, 0, 0) to point in the direction of this vector? Examples using OpenGL would be welcome, but not neccessary. ...
I'm in need of a lightweight library for 2d & 3d vectors and 3x3 & 4x4 matrices. In basic C. Just so I don't reinvent the wheel suboptimally. Any suggestions? ...
how to concat two stl vectors? ...
I've been playing with some algorithms on the internet for a while and I can't seem to get them to work, so I'm tossing the question out here; I am attempting to render a velocity vector line from a point. Drawing the line isn't difficult: just insert a line with length velocity.length into the graph. This puts the line centered at the ...
It seems safe to cast the result of my vector's size() function to an unsigned int. How can I tell for sure, though? My documentation isn't clear about how size_type is defined. ...
I have several std::vector, all of the same length. I want to sort one of these vectors, and apply the same transformation to all of the other vectors. Is there a neat way of doing this? (preferably using the STL or Boost)? Some of the vectors hold ints and some of them std::strings. Pseudo code: std::vector<int> Index = { 3, 1, 2 ...
Edit: This code is fine. I found a logic bug somewhere that doesn't exist in my pseudo code. I was blaming it on my lack of Java experience. In the pseudo code below, I'm trying to parse the XML shown. A silly example maybe but my code was too large/specific for anyone to get any real value out of seeing it and learning from answers ...
From wikipedia: the cross product is a binary operation on two vectors in a three-dimensional Euclidean space that results in another vector which is perpendicular to the plane containing the two input vectors. Given that the definition requires at least three dimensions, how does one calculate the cross product of two 2d vectors?...
Having a vector containing pointers to objects then using the clear function doesn't call the destructors for the objects in the vector. I made a function to do this manually but I don't know how to make this a generic function for any kind of objects that might be in the vector. void buttonVectorCleanup(vector<Button *> dVector){ B...
I want to examine the contents of a std::vector in GDB, how do I do it? Let's say it's a std::vector<int> for the sake of simplicity. ...
Is there a way to resize a std::vector to lower capacity when I no longer need previously reserved space? ...
I want to find in a vector of Object pointers for a matching object. Here's a sample code to illustrate my problem: class A { public: A(string a):_a(a) {} bool operator==(const A& p) { return p._a == _a; } private: string _a; }; vector<A*> va; va.push_back(new A("one")); va.push_back(new A("two")); va.push_b...
I have an array of values that is passed to my function from a different part of the program that I need to store for later processing. Since I don't know how many times my function will be called before it is time to process the data, I need a dynamic storage structure, so I chose a std::vector. I don't want to have to do the standard...