Rust vec drain vec -> usize or * -> vec) A draining iterator over the elements of a `VecDeque`. Also in difference to drain_filter this implementation doesn’t run to completion I have a buffer of type Vec&lt;i32&gt; which I want to write to disk and . For now we'll only vec![x; n], vec![a, b, c, d], and Vec::with_capacity(n), will all produce a Vec with at least the requested capacity. vec -> usize or * -> vec) Search multiple things at once by splitting your query with comma (e. Read more `Vec<T>` 的 draining 迭代器。 根据给定的谓词，对迭代器的元素进行就地重新排序，以使所有返回 true 的元素都在所有返回 false A draining iterator for `Vec<T>`. If you are not familiar with Vec::drain, you can use it like this to “ drain” items out of a Vec (there are similar methods for String, HashMap, and a bunch I don't see it mentioned much, but splice is another handy method in the same family. So, for example, if you are doing a summation, then identity() ought to produce something that represents the zero for your type (but consider just calling I am using Rust stable, which currently makes DrainFilter in std::vec - Rust unavailable. Why clear couldn't be It seems you are caching all errors. There's an unstable nightly feature called drain_filter that Drain. 0 pub fn as What is the difference to call into_iter which returns T?. If such iterator is dropped without exhausting it, all elements are dropped. Of course, both are symmetric, it's just that retain is harder to find if you filter method names by "remove" or "erase" (it does contain "remove" in its description). Is there a nice, clean, simple, O(n) Vec::drain_filter ? I have been trying to write my own impl, but the issue I am running into is the need for T: Clone, which I am trying to avoid. How can I write the contents of the buffer to Struct std::vec::Drain pub struct Drain<'a, T, A = Global> where T: 'a, A: 'a + Allocator, { /* fields omitted */ } A draining iterator for Vec<T>. You can consider drain to be a special case of splice where the input (replace_with) iterator is empty. Instead you will find retain which keeps the elements based on a predicate. You could always remove() entries from one end and add them to the other but the vec would then need to move all the items around which wouldn't be very fast (vecdeque would be more efficient then). As I was working on some revisions to The Rust Programming Language book, 1 I had cause to look at the Vec::drain method, and that led me down a rabbit hole — the rabbit hole we are now going to traverse together. The problem I'm facing is that of ownership. ); Implementations [src] impl<'a, T, A> Drain<'a, T, A> where A: Allocator, [src]1. Example. drain. or you don’t necessarily want to store the removed items in a vector, see Vec::drain. How to split a Vec into two without allocating memory? 0. 83 (emphasis mine): Removes the specified range from the vector in bulk, returning all removed elements as an The solution is to use Vec::drain. Accepted types are: fn, mod, struct, enum, trait, type, macro, and const. drain borrows mutable reference, and returns a drain iterator of elements. Example let mut v = vec![0, 1, 2]; let iter: std::vec::Drain<_> = v. Commented Apr 27, 2017 at 13:18. 46. vec -> usize or * -> vec) fn drain_in_chunks<T>(mut v: Vec<T> { for chunk in v. use std::marker::PhantomData; struct Drain<'a, T: 'a> { // Need to bound the lifetime here, so we do it with `&'a mut Vec<T>` // because that's semantically what we contain. In Rust, it’s more common to pass slices as arguments rather than vectors when you just want to provide read access. This enables us to reuse the allocation of a Vec after claiming ownership over all of its contents. – pigeonhands Reduces the items in the iterator into one item using op. Yeah I don't think there's any easy way to perform an "in-place flatmap either". However, removing many elements using Vec::drain is quite slow (190x slower than ptr::&hellip; I want to remove first N (0 <<< N < Yes, allowing reuse of the allocation is the point of vec. if we drop the value returned by the iterator and then drop the Vec, memory will be twice deallocated. drain() it after a certain time. Rust - return a mutable reference to an element in Vec owned by a struct. It doesn't run to API documentation for the Rust `Drain` struct in crate `ve`. . str,u8 or String,struct:Vec,test) A draining iterator for Vec<T>. vec -> usize or * -> vec) Provides an alternative implementation for Vec::drain_filter. Vec<T> 的 draining 迭代器。 该 struct 由 Vec::drain 创建。 有关更多信息，请参见其文档。 Example Source of the Rust file `library/alloc/src/vec/drain_filter. filter(condition). g. In fact you would have the same issue here: the first item would replace the one being vec::Drain; Rc; thread::scoped::JoinGuard; Drain. rs`. §Example v. The vector will be able to hold at least capacity elements without reallocating. 9. If you look at the interface of Vec, you will not find a method that erases some elements based on a predicate. Not in stable Rust 1. If we drop the O(n) time, it is easy to do via Vec::remove, but this has worst case O(n^2). This struct is created by the drain method on Vec. However, unlike the into_iter() method, which takes the collection by value and consumes it, drain merely borrows a mutable references to the collection, and when the iterator is dropped, it removes any remaining elements from the collection, and leaves it empty. The only panic that can happen in that code snippet is the one you have pointed out, and you are avoiding it by checking the vector length before calling drain. Read more You can use Vec::drain to remove elements from your vector and create an iterator from the removed elements: struct Container{ vec : Vec<f32>, } fn empty Is there a faster/shorter way to initialize variables in a Rust struct? 7. Prefix searches with a type followed by a colon (e. Read more Drain is largely the same as IntoIter, except that instead of consuming the Vec, it borrows the Vec and leaves its allocation untouched. It is important to note that although the returned vector has the minimum capacity specified, the vector will have a zero On page 327 of Programming Rust you can find the following statement. fn:) to restrict the search to a given type. The e_ prefix is to prevent name collision/confusion as drain_filter might be stabilized as drain_where. collect() returns the correct value for drained but empties the whole vector. A draining iterator for Vec<T>. into_iter() What is a drain method on iterator used for? It is used to remove a range of elements from a vector, optionally giving you the elements in the range. This method is allowed to allocate for more elements than capacity. If len == capacity, (as is the case for the vec! macro), then a Vec<T> can Then you could start with a Vec<&'long str>, get a Drain<'_, &'long str> from the drain method, coerce it to a Drain<'_, &'short str>, obtain a &mut [&'short str], put a short-lived A draining iterator for Vec<T>. into_iter takes the collection by value and consumes it. Consider that reserve reserve has been called prior, and that the Vec/VecDeque already have space for the elements. See its documentation for more. Read more A draining iterator for `Vec<T>`. Also in difference to drain_filter this implementation doesn't run to completion Reduces the items in the iterator into one item using op. Why I want to do this is, because I want to move the chunks into a function. Import VecDrainWhereExt to extend Vec with an e_drain_where method which drains all elements where a predicate indicates it. Edit: For clarification, what happens, at memory level, with the following code? Are the contents copied I'm currently draining a vec to iterate it, so I can hopefully reuse it's allocated memory when adding to it later now, my question is, does it actually keep the memory allocated, and if not, what's a better/faster way of doing this (assuming I need to iter over the entire vec) A alternate Vec::drain_filter implementation, slightly diverging from the std's implementation. Search functions by type signature (e. now the Vec owns the heap allocated memory, but the RawValIter (virtually) Search Tricks. This crate provides an extension trait adding a e_drain_where method (the e_ prefix is used to prevent name collisions with std as the currently drain_filter might be stabilized as drain_where). Drain is largely the same as IntoIter, except that instead of consuming the Vec, it borrows the Vec and leaves its allocation untouched. I'm confused at what it means it Drain is largely the same as IntoIter, except that instead of consuming the Vec, it borrows the Vec and leaves its allocation untouched. See its documentation for more. Constructs a new, empty Vec<T> with at least the specified capacity. This struct is created by Vec::drain. Search Tricks. For now we'll only implement the "basic" full-range version. An iterator method that reduces the iterator's elements to a single, final value, starting from the back. e_drain_where as one large difference to drain filter. ) over std::mem::take(&mut vec). ). 33. note the line with comments about mem::forget() safety inside the Vec::drain() function? it sets len to zero, this semantically transfers the ownership of the Vec's contents to the RawValIter. Provides an alternative implementation for Vec::drain_filter. Let's move on to Drain. So, for example, if you are doing a summation, then identity() ought to produce something that represents the zero for your type (but consider just calling Could Vec::drain() be combined with slice destructuring to provide the move+destructure semantics? – user4815162342. Reorders the elements of this iterator in-place according to the given predicate, such that all those that return true precede all those that return false. The same goes for String and &str. Returns the number of true elements found. chunks(2){ do_something(chunk)} } where I remove chunks of size two from v in each iteration. drain(. drain is a collections API that moves data out of the container without consuming the container. 0. The argument identity should be a closure that can produce “identity” value which may be inserted into the sequence as needed to create opportunities for parallel execution. In Rust, do the methods extend and drain from Vec and VecDeque copy the contents of the items, or are the items moved in like in a list?. Here’s how the docs describe Vec::drain as of Rust 1. If capacity is 0, the vector will not allocate. How to bind multiple fields of a boxed struct without getting "use moved value" error? 161. However, I can't move elements from a vector without removing them. .