python numpy euclidean distance calculation between matrices of row vectors
To get the distance you can use the norm method of the linalg module in numpy: np.linalg.norm(x – y)
vector
How to convert vector iterator to int in C++
You need to use standard function std::distance index = std::distance( myvector.begin(), it ); if ( index < myvector.size() ) { // do something with the vector element with that index } Try always to use std::distance even with random access iterators. This function is available in the new and old C++ Standards.
Multi-dimensional vector
vector<vector<int> > a; If you want to define the rows and columns, vector<vector<int> > a{{11, 2, 4}, {4, 5, 6}, {10, 8, -12}};
Direction of two points
Answer 1: it is Vector(x2-x1,y2-y1) Answer 2: Normalizing means to scale the vector so that its length is 1. It is a useful operation in many computations, for example, normal vectors should be specified normalized for lighting calculations in computer graphics. The normalized vector of v(x,y) is vn(x/Length(v), y/length(v)). HTH
“Cannot allocate an object of abstract type” error
In C++ a class with at least one pure virtual function is called abstract class. You can not create objects of that class, but may only have pointers or references to it. If you are deriving from an abstract class, then make sure you override and define all pure virtual functions for your class. From … Read more
Does clearing a vector affect its capacity?
No, it doesn’t. The capacity of a vector never decreases. That isn’t mandated by the standard but it’s so both in standard library implementations of VC++ and g++. In order to set the capacity just enough to fit the size, use the famous swap trick vector<T>().swap(foo); In C++11 standard, you can do it more explicitly: … Read more
c++ stl what does base() do
base() converts a reverse iterator into the corresponding forward iterator. However, despite its simplicity, this correspondence is not as trivial as one might thing. When a reverse iterator points at one element, it dereferences the previous one, so the element it physically points to and the element it logically points to are different. In the … Read more
C++ vector literals, or something like them
In C++0x you will be able to use your desired syntax: vector<vector<vector<string> > > vvvs = { { {“x”,”y”, … }, … }, … }; But in today’s C++ you are limited to using boost.assign which lets you do: vector<string> vs1; vs1 += “x”, “y”, …; vector<string> vs2; … vector<vector<string> > vvs1; vvs1 += vs1, … Read more
small string optimization for vector?
Boost 1.58 was just released and it’s Container library has a small_vector class based on the LLVM SmallVector. There is also a static_vector which cannot grow beyond the initially given size. Both containers are header-only. facebook’s folly library also has some awesome containers. It has a small_vector which can be configured with a template parameter … Read more