How do I calculate the normal vector of a line segment? [closed]
If we define dx = x2 – x1 and dy = y2 – y1, then the normals are (-dy, dx) and (dy, -dx). Note that no division is required, and so you’re not risking dividing by zero.
vector
When vectors are allocated, do they use memory on the heap or the stack?
vector<Type> vect; will allocate the vector, i.e. the header info, on the stack, but the elements on the free store (“heap”). vector<Type> *vect = new vector<Type>; allocates everything on the free store. vector<Type*> vect; will allocate the vector on the stack and a bunch of pointers on the free store, but where these point is … Read more
Convert data.frame column to a vector?
I’m going to attempt to explain this without making any mistakes, but I’m betting this will attract a clarification or two in the comments. A data frame is a list. When you subset a data frame using the name of a column and [, what you’re getting is a sublist (or a sub data frame). … Read more
How to initialize a vector in C++ [duplicate]
With the new C++ standard (may need special flags to be enabled on your compiler) you can simply do: std::vector<int> v { 34,23 }; // or // std::vector<int> v = { 34,23 }; Or even: std::vector<int> v(2); v = { 34,23 }; On compilers that don’t support this feature (initializer lists) yet you can emulate … Read more
When should I choose Vector in Scala?
As a general rule, default to using Vector. It’s faster than List for almost everything and more memory-efficient for larger-than-trivial sized sequences. See this documentation of the relative performance of Vector compared to the other collections. There are some downsides to going with Vector. Specifically: Updates at the head are slower than List (though not … Read more
How to initialize std::vector from C-style array?
Don’t forget that you can treat pointers as iterators: w_.assign(w, w + len);
Thou shalt not inherit from std::vector
Actually, there is nothing wrong with public inheritance of std::vector. If you need this, just do that. I would suggest doing that only if it is really necessary. Only if you can’t do what you want with free functions (e.g. should keep some state). The problem is that MyVector is a new entity. It means … Read more
How do I print the elements of a C++ vector in GDB?
With GCC 4.1.2, to print the whole of a std::vector<int> called myVector, do the following: print *(myVector._M_impl._M_start)@myVector.size() To print only the first N elements, do: print *(myVector._M_impl._M_start)@N Explanation This is probably heavily dependent on your compiler version, but for GCC 4.1.2, the pointer to the internal array is: myVector._M_impl._M_start And the GDB command to print … Read more
What is the best way to concatenate two vectors?
AB.reserve( A.size() + B.size() ); // preallocate memory AB.insert( AB.end(), A.begin(), A.end() ); AB.insert( AB.end(), B.begin(), B.end() );
C++ STL Vectors: Get iterator from index?
Try this: vector<Type>::iterator nth = v.begin() + index;