An Existing Size-Lazy Vector Type In Haskell
As Jake McArthur noted in the comments: “If it’s just a function, then I recommend just using one of the existing memoization packages like MemoTrie or data-memocombinators. They should make it easy.”
vector
PyTorch element-wise product of vectors / matrices / tensors
Given two tensors A and B you can use either: A * B torch.mul(A, B) A.mul(B) Note: for matrix multiplication, you want to use A @ B which is equivalent to torch.matmul().
Rust pattern matching over a vector
You need slice patterns: fn vec_alt<T>(vals: Vec<T>) -> &’static str { match vals[..] { [a, b] => “two elements”, [a, b, c] => “three elements”, _ => “otherwise”, } }
What is the idiomatic way to remove the first N elements in a mutable Vec?
Use drain to remove multiple contiguous elements from a vector at once as efficiently as possible (the implementation uses ptr::copy to move the elements that remain): let mut v = vec![1, 2, 3, 4]; v.drain(0..2); assert!(v == vec![3, 4]); Regarding #2, it is not feasible to avoid shifting the remaining elements. That optimization would require … Read more
std::vector: vec.data() or &vec[0]
data() is brand new to C++11, that’s why you don’t see it as often. The idea of using &vec.front() never even occurred to me, probably because I use operator[] alot more often than front() (almost never). I imagine it’s the same for other people.
C++ sizeof Vector is 24?
While the public interface of std::vector is defined by the standard, there can be different implementations: in other words, what’s under the hood of std::vector can change from implementation to implementation. Even in the same implementation (for example: the STL implementation that comes with a given version of Visual C++), the internals of std::vector can … Read more
Using find_if on a vector of object
That’s not how predicates work. You have to supply either a free function bool Comparator(const MyClass & m) { … }, or build a function object, a class that overloads operator(): struct MyClassComp { explicit MyClassComp(int i) n(i) { } inline bool operator()(const MyClass & m) const { return m.myInt == n; } private: int … Read more
Keeping the first N elements of a std::vector and removing the rest
Yes, you can use std::vector::resize, which just truncates if the length of the vector is greater than n. See here: http://www.cplusplus.com/reference/vector/vector/resize/ std::vector<int> myvector; for (int i=1;i<1000;i++) myvector.push_back(i); myvector.resize(50); // myvector will contain values 1..50
Where does a std::vector allocate its memory?
Does a std::vector allocate memory for its elements on the heap? Yes. Or more accurately it allocates based on the allocator you pass in at construction. You didn’t specify one, so you get the default allocator. By default, this will be the heap. But how does it free that heap memory? Through its destructor when … Read more
C++, Sort One Vector Based On Another One [duplicate]
An alternative to consolidating the names and scores into a single structure is to create an index list and sort that: std::vector<int> indices(Names.size()); std::iota(indices.begin(), indices.end(), 0); std::sort(indices.begin(), indices.end(), [&](int A, int B) -> bool { return Score[A] < Score[B]; }); Now indices can be used to index Names and Scores in the desired sorted order.