I’m using multitreading and want to merge the results. For example: std::vector<int> A; std::vector<int> B; std::vector<int> AB; I want AB to have to contents of A and the contents of B in that order. What’s the most efficient way of doing something like this? 11 Answers 11
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. 5 Answers 5
So, I wrote a bunch of code that accesses elements in an stl vector by index[], but now I need to copy just a chunk of the vector. It looks like vector.insert(pos, first, last) is the function I want… except I only have first and last as ints. Is there any nice way I can … Read more
I’ve always thought it’s the general wisdom that std::vector is “implemented as an array,” blah blah blah. Today I went down and tested it, and it seems to be not so: Here’s some test results: UseArray completed in 2.619 seconds UseVector completed in 9.284 seconds UseVectorPushBack completed in 14.669 seconds The whole thing completed in … Read more
I have found an interesting performance regression in a small C++ snippet, when I enable C++11: #include <vector> struct Item { int a; int b; }; int main() { const std::size_t num_items = 10000000; std::vector<Item> container; container.reserve(num_items); for (std::size_t i = 0; i < num_items; ++i) { container.push_back(Item()); } return 0; } With g++ (GCC) … Read more
In our C++ course they suggest not to use C++ arrays on new projects anymore. As far as I know Stroustroup himself suggests not to use arrays. But are there significant performance differences? 20 Answers 20
This question already has answers here: how does multiplication differ for NumPy Matrix vs Array classes? (8 answers) Closed 8 years ago. When I multiply two numpy arrays of sizes (n x n)*(n x 1), I get a matrix of size (n x n). Following normal matrix multiplication rules, an (n x 1) vector is … Read more
I have to split a vector into n chunks of equal size in R. I couldn’t find any base function to do that. Also Google didn’t get me anywhere. Here is what I came up with so far; x <- 1:10 n <- 3 chunk <- function(x,n) split(x, factor(sort(rank(x)%%n))) chunk(x,n) $`0` [1] 1 2 3 … Read more
I noticed in Effective STL that vector is the type of sequence that should be used by default. What’s does it mean? It seems that ignore the efficiency vector can do anything. Could anybody offer me a scenario where vector is not a feasible option but list must be used? 17 Answers 17
What are the good ways of finding the sum of all the elements in a std::vector? Suppose I have a vector std::vector<int> vector with a few elements in it. Now I want to find the sum of all the elements. What are the different ways for the same? 13 Answers 13
