Checking if v contains the element x: #include <algorithm> if(std::find(v.begin(), v.end(), x) != v.end()) { /* v contains x */ } else { /* v does not contain x */ } Checking if v contains elements (is non-empty): if(!v.empty()){ /* v is non-empty */ } else { /* v is empty */ }
std::vector is a template class that encapsulate a dynamic array1, stored in the heap, that grows and shrinks automatically if elements are added or removed. It provides all the hooks (begin(), end(), iterators, etc) that make it work fine with the rest of the STL. It also has several useful methods that let you perform … Read more
vector<T>::const_iterator first = myVec.begin() + 100000; vector<T>::const_iterator last = myVec.begin() + 101000; vector<T> newVec(first, last); It’s an O(N) operation to construct the new vector, but there isn’t really a better way.
Actually, the first one is a bad idea. Use either the second one, or this: struct greater { template<class T> bool operator()(T const &a, T const &b) const { return a > b; } }; std::sort(numbers.begin(), numbers.end(), greater()); That way your code won’t silently break when someone decides numbers should hold long or long long … Read more
If you have a C++11 compiler, I would suggest using a range-based for-loop (see below); or else use an iterator. But you have several options, all of which I will explain in what follows. Range-based for-loop (C++11) In C++11 (and later) you can use the new range-based for-loop, which looks like this: std::vector<char> path; // … Read more
If you have a C++11 compiler, I would suggest using a range-based for-loop (see below); or else use an iterator. But you have several options, all of which I will explain in what follows. Range-based for-loop (C++11) In C++11 (and later) you can use the new range-based for-loop, which looks like this: std::vector<char> path; // … Read more
Differences Vectors are synchronized, ArrayLists are not. Data Growth Methods Use ArrayLists if there is no specific requirement to use Vectors. Synchronization If multiple threads access an ArrayList concurrently then we must externally synchronize the block of code which modifies the list either structurally or simply modifies an element. Structural modification means addition or deletion … Read more
The component type of containers like vectors must be assignable. References are not assignable (you can only initialize them once when they are declared, and you cannot make them reference something else later). Other non-assignable types are also not allowed as components of containers, e.g. vector<const int> is not allowed.
There’s a fairly simple trick to do so, since the spec now guarantees vectors store their elements contiguously: std::vector<double> v; double* a = &v[0];
You can just use table(): > a <- table(numbers) > a numbers 4 5 23 34 43 54 56 65 67 324 435 453 456 567 657 2 1 2 2 1 1 2 1 2 1 3 1 1 1 1 Then you can subset it: > a[names(a)==435] 435 3 Or convert it into … Read more