Rust map with index. Indices The key-value pairs are indexed in a compact range without holes in the range 0. get_index looks up the key-value pair by index. Complexity Internally, IndexSet<T, S> just holds an IndexMap<T, (), S>. It preserves insertion order (except after removals), and it allows lookup of entries by either hash table key or numerical index. Notes about side effects The map iterator implements DoubleEndedIterator, meaning that you can also map backwards: let v: Vec<i32> = vec! [1, 2, 3]. What is the best/most Rust-y way of getting a (mutable) iterator over the elements of w which are indexed by the elements of v? In essence, this is a general, non-contiguous slice. Feb 20, 2024 · Your examples so far have all been sorted, so binary_search may or may not be better (perhaps depending on how large these slices are; [1] test if you care). For more about the concept of iterators generally, please see the module-level documentation. Contribute to lun3x/multi_index_map development by creating an account on GitHub. `IndexMap` is a hash table where the iteration order of the key-value pairs is independent of the hash values of the keys. enumerate() I was able to access the iterator using a map of the vec, but received an error: unused `std::iter::Map` that must be used note: `#[warn(unused_must_use)]` on by default note: iterators are lazy and do nothing It internally is based on a Vec, where each element either stores a value, or stores the index of the next free element. * amortized similar to Vec::push() (triggers a resize when len() == capacity I have read How to iterate a Vec<T> with the indexed position? where the answer is to use enumerate in a for-loop. A couple of demonstrations: let u = vec![1, 2, 3]; let v: Vec<_> = u. println!("Index: {}, Value: {}", i, x); let v = vec![1, 2, 3];: creates a vector v with elements 1, 2, and 3. map(f). This method returns a tuple of the index and the value of the element. The range may be any type that implements RangeBounds<usize>, including all of the std::ops::Range* types, or even a tuple pair of Bound start and end values. Jan 4, 2025 · In the world of programming, keeping data organized is crucial, particularly when dealing with key-value pairs using hash maps. See also entry if you you want to insert or modify or if you need to get the index of the corresponding key-value pair. Since it accommodates for empty elements in between, it can perform O (1)* inserts and O (1) removals from any index. Compare/contrast their documentation and examples. Because of this, the randomness of the Suppose I have v : Vec<usize> and I happen to know that all the v are < k, the length of some (mutable) vector w. Sep 14, 2025 · This is because map() is still being called lazily on each item, but we are popping items off the back of the vector now, instead of shifting them from the front. get_index looks up the value by index. ). This allows nice things such as let value = v[index] if the type of value implements Copy. The algorithm is randomly seeded, and a reasonable best-effort is made to generate this seed from a high quality, secure source of randomness provided by the host without blocking the program. In particular, you may want to know how to implement Iterator. Unlike traditional HashMap collections, which do not preserve the order of entries, Rust provides a smart Sep 14, 2025 · Used for indexing operations (container[index]) in immutable contexts. Feb 20, 2021 · How can I get the index of the current element? I have tried for el, i in list for {el, i} in list for (el, i) in list. This is the main iterator trait. For example, the method . collect::<Vec<_>>(); . rev (). The “free” indices essentially make a singly linked list. Scan through each key-value pair in the map and keep those where the closure keep returns true. into_iter (). The map function in Rust is a powerful and commonly used function that allows you to transform elements of an iterator by applying a closure or function to each element. Examples The following example implements Index on a read Clears the IndexMap in the given index range, returning those key-value pairs as a drain iterator. 30+ for development builds, and Rust 1. get_full looks up the index for a key, and the method . Otherwise, the new key-value pair is inserted at the sorted position, and (index, None) is returned. How it works It internally is based on a Vec, where each element either stores a value, or stores the index of the next free element. Inspired by C++/Boost Multi-index Containers but redesigned for a more idiomatic Rust API. Simple and flexible multi-index containers. This crate implements compact map and set data-structures, where the iteration order of the keys is independent from their hash or value. collect() is probably the most magic part of it, and allows you to collect all the elements of the iterator IndexMap index-map is a crate I made which provides a map with automatically generated usize s as keys. Features It automatically generates (and recycles) unique usize s as keys, `IndexMap` is a hash table where the iteration order of the key-value pairs is independent of the hash values of the keys. If the sorted key is found in the map, its corresponding value is updated with value, and the older value is returned inside (index, Some (_)). Rust Version This version of indexmap requires Rust 1. This struct is created by the map method on Iterator. To drain the map entirely, use RangeFull like map. A pure-Rust hash table which preserves (in a limited sense) insertion order. May 21, 2025 · Rust library useful for storing structs that needs to be accessed through various different indexes of the fields of the struct. I thought maybe I could create an index of the elements I w The [MutableKeys] [map::MutableKeys] trait, which gives opt-in mutable access to hash map keys. This shifts down all entries following the drained range to fill the gap, and If no equivalent key existed in the map: the new key-value pair is inserted, last in order, and (index, None) is returned. The order does not depend on the keys or the hash function at all. See its documentation for more. Clears the IndexMap in the given index range, returning those key-value pairs as a drain iterator. If you have multiple entries with the same value and care which is returned, you may want partition_point instead of binary_search. Sep 14, 2025 · A hash map implemented with quadratic probing and SIMD lookup. Mapping with index in Rust can be done using the enumerate() method on an iterator. Jun 8, 2022 · I have a Vec<f64> and I am trying to get say every 7th element of the vector till I run out of bounds, into another Vec<f64>. By default, HashMap uses a hashing algorithm selected to provide resistance against HashDoS attacks. get_full looks up the index for a value, and the method . The elements are visited in order, and remaining elements keep their order. container[index] is actually syntactic sugar for *container. collect (); assert_eq! (v, [4, 3, 2]); Run But if your closure has state `IndexMap` is a hash table where the iteration order of the key-value pairs is independent of the hash values of the keys. If a mutable value is requested, IndexMut is used instead. map (|x| x + 1). But if I don't use a for-loop like this: fn main () { let v = vec! [1; 1 Rust map search and generator to find the perfect map for your server and view animal, node and resource heatmaps. 36+ for using with alloc (without std), see below. These methods provide clear pathways to make the most out of vector data by elegantly expressing logical transformations and mutations, helping you write expressive, safe, and high-performance code. This shifts down all entries following the drained range to fill the gap, and A trait for dealing with iterators. Thus the complexity of the two are the same for most methods. collect(); let u = vec![1, 2, 3]; let v = u. iter(). The key-value pairs have a consistent order that is determined by the sequence of insertion and removal calls on the map. 18 or later, or 1. len (). self. Jan 4, 2025 · Leveraging map, iter_mut, and collect efficiently streamlines data transformation in Rust. A map of `usize` to value, which allows efficient O (1) inserts, O (1) indexing and O (1) removal. An iterator that maps the values of iter with f. . Computes in O (1) time (amortized average). map(|&x| x + 1). Rust likes to be more general than that; mapping is done over iterators, rather than over solely vectors or slices. drain(. Its basically meant for use cases where you need to associate unique ids with some object, but the actual id itself is irrelevant outside the map. index(index), but only when used as an immutable value. Examples use indexmap::IndexSet; // Collects which letters appear in a sentence. i1nvuy fjcsg 1hs eu5 wn sqz eb vmj vl fmgkad