Rust hashmap from vector. Either by let mut victim = vec; or in the argument list by: fn vec_to_set(mut vec: Vec<u8>) . item: String, Jun 12, 2021 · This means that we can expect that the key-value pairs associated with the same hash are tightly packed in memory, and iterating over them should be very similar to iterating over a vector: regular progression (with some skips however) very friendly with cache prefetch. The data is expected to be in the following form: Oct 1, 2022 · If I understand your question correctly, you are trying to, given a vector [n, m], insert a (key, value) pair into a HashMap where the key is n and the value is another HashMap, containing the (key, value) pair, (m, 0). let mut to_remove = Vec::new(); for (key, value) in &*map {. collect(); The code above will create a BinaryHeap of references. §No-std support. I'm trying to insert a (i32, (usize, usize)) pair into the last hashmap which exists in my vector of hashmaps using the following code: let mut boards: Vec<HashMap<i32, (usize, usize)>>; for line in file_it. In a vector, the indices have to be integers; in a HashMap they can be (almost) any type. For example, “Add Sally to Engineering” or “Add Amir to Sales. if vec[i as usize][0] == 0 {. optimizing hashmaps even more— 2021-05-08. Looking through the source of the std libraries you can find the implementation of PartialEq for those different collections: HashMap iterate over all key/value pair and check if the other map has a corresponding entry for that key, and then check if those value are equal: source. Mar 7, 2015 · Removing entries from a HashMap based on value. Version 1 We use from_iter and pass the result of iter () called on the HashMap. Many different programming languages support this kind of data structure, but often use a different name, such Jan 21, 2022 · HashMap::new(), |mut map, word| { *map. That is, in JSON: { n: { m: 0 } } As one commenter mentioned, you'll need to create the second map. unwrap(). I tried this in a multitude of ways, but continued to Sep 22, 2021 · The Rust Programming Language Forum Elegant way to convert vec to map. See its documentation for more. tl;dr: Vec is like an array, searching for the correct String is an O (n) operation. Nov 15, 2021 · Rust – HashMaps. I think you can clone the keys directly, instead of the hashmap, and move the cloned keys to the closure. (iter_map_windows #87155) Calls the given function f for each contiguous window of size N over self and returns an iterator over the outputs of f. case_insensitive_hashmap. 7. When I run the code in debug mode it takes about 100s but in release mode, the speed is very acceptable for me at approx 7s! Oct 8, 2020 · The Values struct is defined as. iter () then produces references to the elements of instances, so instance: &&mut String. to obtain the struct I want using the "regex_key". iter(). Add a comment. use std::collections::HashMap; fn find_key_for_value<'a>(map: &'a HashMap<i32, &'static str>, value: &str) -> Option<&'a i32> {. May 23, 2019 · Hello everyone! I have a HashMap with a byte vector as key. If you wanted to avoid the 48 bytes, you would use a Box. use std::collections::HashSet; #[derive(Hash, Eq, PartialEq, Debug)] struct Viking {. 2k 1. keys (). An iterator over the values of a HashMap. I'll make that more clear in the question. If you don't need this guarantee, you can use a simpler hash function. Each element access needs two pointer indirection – first, following the outer point on the stack to the heap allocation containing the pointers to the individual rows, and then following the pointer to the right row. This way of working with iterators also means that you often won’t even need to create intermediate vectors where in other languages or with other techniques you would; this is more efficient and HashMap keys can be booleans, integers, strings, or any other type that implements the Eq and Hash traits. Follow How to build a HashMap of Vectors in Rust? 1. The hash map will be able to hold at least capacity elements without reallocating. More on this in the next section. Sorted by: 17. Jan 17, 2020 · 12. We learn the module needed to enable us to use a hashmap. Hash tables are usually implemented using arrays. Each key is associated with a single value. The closure returns the value that the accumulator should have for the next iteration. It should be at the top of the program. Like slices, their size is not known at compile time, but they can grow or shrink at any time. The former is a proper iterator adaptor that returns a transforming iterator which turns references into cloned values; the latter (what you currently have) is just a regular call to clone, which knows nothing about iterators, and merely clones the value it is being called on (in your case, the iterator itself). What is a HashMap. insert(String::from("two"), 2); map. Creates an empty HashMap with the specified capacity, using hash_builder to hash the keys. globalflea September 22, Nested HashMap to key value Vec. 4k 1. Currently I'm trying to figure out how to use contains_key with a byte string literal. We also learn how to instantiate a new hashmap, add, remove and access elements as singles or in a loop, as well as how to check if an element exists in a hashmap. Since it implements FromIterator, you can do. String is likewise available. The conversion function was just an iteration over the Mar 24, 2023 · HashMap to vec. The task is to find the funniest words in a given text as ranked by the funny_score method. 6: 910: January 29, 2021 Creating a HashMap in Rust. 1. However, if the vector’s length is increased to 11, it will have to reallocate, which can be slow. perhaps you can have a try with this: if let Some (max) = a_hash_map. Where vectors store values by an integer index, HashMap s store values by key. Oct 18, 2019 · For example, an iterator of Ts can be collected to Vec<T>, of chars can be collected to a String, of (K, V) pairs to a HashMap<K, V>, and so forth. Oct 1, 2016 · FYI: in your first code, you don't need to clone the vector, you just need to declare it as mutable. pub struct HashMap<K, V, S = DefaultHashBuilder, A: Allocator = Global > { /* private fields */ } A hash map implemented with quadratic probing and SIMD lookup. clone(). This is useful if you keep the Vec around, especially since you don't need to clone the key. cloned(), not . Sep 21, 2021 · The program then does the job of merging these hashmaps into a single hashmap and returns an output of those pairs. and the second value of the vector should be smaller than all second value of each vector key. The type HashMap<K, V> stores a mapping of keys of type K to values of type V. We actually can move the elements out of the vector! Assuming you don't need to keep the vector, we can use the drain() method to move all the elements out of the vector and into a hashmap like so: May 23, 2015 · Currently, HashMap does not implement IndexMut, while Vec does. We can place the keys, values, or both keys and values at once into a vector. Jan 1, 2021 · first value of the vector should be greater than all first value of each vector key. Vectors are re-sizable arrays. I'm generating a HashMap as in this playground / below code. Using this macro, it is possible to have static s that require code to be executed at runtime in order to be initialized. contains_key(b"xyz") { println!("Something"); } } Unfortunately that doesn't quite work, I get the Aug 17, 2017 · Once the loop is complete, the ownership of the structure is relinquished and you can use it again. This includes anything requiring heap allocations, like vectors or hash maps, as well as anything that requires function calls to be computed. 0. It does this via a hashing function, which determines how it places these keys and values into memory. In our last post we took a look at possible ways we could improve the ergonomics of Rust's refcounting APIs. This hash function is very fast for all types of keys, but this Nov 21, 2021 · This answer looks good. So I get the mut map is the accumulator and I get that split How to make a rust backround image photoshop What are the meanings of the phrases DAY, RWYCC, 6/6/6 in ATIS? Unique factorization of ideals in a quadratic field Apr 26, 2018 · I am doing the third exercise of the second edition of the Book - chapter 8. This makes sense since we can only clone the HashMap if we can clone its content. Improve this question. 1 instances. Feb 8, 2015 · Starting with Rust 1. conclusion. However, there is an easy way to convert the values into a BinaryHeap. Iterate over the entries of the HashMap, find the entry matching the value, and map to the key. map. Jun 5, 2019 · The Rust Programming Language Forum How can I add the a hash map to the b? HashMap with vector values. Feb 18, 2020 · I'm trying to set a constant, predefined hash map in Rust. I want to find the best way to merge the hashmaps in this vector, making a single hashmap that contains all the unique keys from all the hashmaps I start with, while adding together their values. Mar 17, 2024 · The easiest way to use HashSet with a custom type is to derive Eq and Hash. Jul 27, 2023 · iter produces an iterator of references. Can I build a hashmap in Rust a bit like this: hashmap![("key", "value")] without creating a separate variable and calling . In particular, a hashmap where you haven’t removed any elements will grow (AFAICT, as of this writing) using a doubling strategy and keeping the map always up to a maximum of 87. find (| | ) etc. 5 { match file_it. Like slice::windows () , the windows during mapping overlap as well. get provides a reference because in Rust you cannot simply return the actual value that is in the hash table - you need to either clone it (make a copy, potentially expensive), remove it from the container and transfer it to the caller, or return a reference to the value Aug 23, 2023 · Vector of tuples: You can also use a Here are the main operations you can perform on a hashmap in Rust: Insertion: Adding a key-value pair to the hashmap. Jan 18, 2020 · Sort HashMap data by keys. into_iter(). How can I sort the generated result map based on the keys , in my case based on Dimension, Location : Nov 19, 2018 · Using a hash map and vectors, create a text interface to allow a user to add employee names to a department in a company. Pushing 10 or fewer elements onto the vector will not change its capacity or cause reallocation to occur. let count_b: BTreeMap<&u32,&char> = count. – Lukas Kalbertodt Jun 26, 2022 · How can I turn a HashMap into a string in rust? Turn a Vector<HashMap<String, String>> Into a String or a JSON Object. Having millions of empty hash maps in the vector easily makes my program consume tens of GB. Jun 28, 2021 · for (key, instances) in duplicates invokes the IntoIterator trait on HashMap<String, Vec<&mut String>>, with. help. Apr 15, 2023 · Empty HashMap still requires 48 bytes according to size_of, while an option only requires 8. Aug 21, 2022 · 1 Answer. . Cross referencing to Rust forum, I'm generating a HashMap as in this playground / below code. The commit that removed HashMap's IndexMut implementation states: This commit removes the IndexMut impls on HashMap and BTreeMap, in order to future-proof the API against the eventual inclusion of an IndexSet trait. 5% full, so you’d be Jun 12, 2019 · Hello, Rust newbie here (I'm about 2-3 weeks in). Sorted by: 3. You can use it to create a vector of N strings: vec::from_elem(N, ~"") This will create a vector of empty boxed strings. The concept of HashMap is present in almost all programming languages like Java, C++, Python, it has key-value pairs and through key, we can get values of the map. collect(); If capacity is 0, the hash map will not allocate. May 29, 2021 · A HashMap is like a vector, but more general. A nitty thing is cloning HashMap will clone its keys, values and hasher. HashMap<K, V> to a const or Creating a Rust HashMap from a vector of tuples is a simple process. The capacity indicates how much memory is reserved for the vector. lines() { // file_it is a BufReader file iterator if line. use std::collections::HashMap; pub const Countries: HashMap<&str, &str> = [ ("UK", "United Kingdom"), ("US", "United States") ]. 7k 4 35 52. let mut a: HashSet<i32> = vec![1i32, 2, 3]. is_empty() { boards. Jun 19, 2015 · Is there a way to consume a HashMap and get a vector of values in Rust? 1. If you need an ordered map for some reason, you should use indexmap . – Dec 17, 2019 · As the comment suggested this is a slightly unfortunate interaction of how Rust looks up methods via references / autoderef: The implementation of Clone on HashMap requires the keys and the values (and the hasher) to be Clone as well. Shepmaster. so instances: Vec<&mut String>. 2k silver badges 1. Like vectors, HashMap s are growable, but HashMaps can also shrink themselves when they have excess space. iter (). However removing elements from the map is reflected on later . Originally, each tuple was unique, and the user would pass a pair of a string and a char, so I had a hashmap of which was of the form HashMap<(String, Option<char>), String>. Sep 18, 2020 · Unlike Python's dict, Rust's "built-in" hashmap is not ordered, so sorting it has no effect. The following example code creates a HashMap from a vector of tuples: let mut map = HashMap::new(); let v = vec![(1, "a"), (2, "b"), (3, "c")]; for ( key, value) in v {. I was looking at Vectors and HashMaps, and made me wonder if I can create a HashMap of references to a vector's elements. SipHash is designed to avoid denial-of-service attacks based on predicting hash collisions, which is an important security property for a hash function used in a hash map. intersection: get all the elements that are only in both sets. Dec 19, 2019 · 1 Answer. or_insert(Vec::new()) . That might not be efficient if what you need is the clone of the keys. HashMap. I've written the following code ( + demo) to remove entries from a HashMap based on value. You can't use HashMap or HashSet in a no_std environment because to avoid hash difference: get all the elements that are in the first set but not the second. This struct is created by the values method on HashMap. How can I sort the generated result map based on the keys, in my case based on Dimension, Location: use std::collections::HashMap; #[derive(Debug, Eq, PartialEq, Hash, Clone)] struct Dimension {. hashmaps and hashing algorithms. 4k Mar 17, 2024 · If capacity is 0, the hash map will not allocate. cloned(). Converts a HashMap<K, V> to a const or constant [(K, V); N] string representation, where N is the number of key-value pairs in the input map object. let tmp = x. A vector is represented using 3 parameters: pointer to the data. A naive implementation would pass the String to a hashing function which would turn it into a number between 0 and n, where n is the size Mar 19, 2022 · I tried to create a simple procedural macro using syn to aid in parsing expressions, but it chokes on the Expr : Expr syntax because it attempts to eagerly parse the first expression as a type ascription expression which is a yet-to-be-completed feature. length. This code example goes from a HashMap to 3 different kinds of vectors. level) . values(). 410k 106 106 gold badges 1. This is what I'm trying to do: use std::collections::HashMap; fn main() { let mut company: HashMap<String Feb 11, 2014 · It is a pointer, and pointers can't be equal to null in Rust, which would have been the most natural default value for a pointer. Dec 2, 2019 · What you can do with signing up. let mut users_by_level: HashMap<&str, Vec<&User>> = HashMap::new(); for user in users. Most methods that have a key parameter Jan 1, 2022 · Rust's HashMap by default uses an implementation of SipHash as the hash function. Apr 14, 2020 · Iterate over 2D Vector and store data in hash map. 56, you can use from () to build a Hashmap from an array of key-value pairs. Vec is a 2D vector. let heap: BinaryHeap<_> = map. In this post we'll be looking at Hashmap: how it's currently Jan 13, 2022 · Budding Rustacean here. ” Then let the user retrieve a list of all people in a department or all people in the company by department, sorted alphabetically. [ −] A macro for declaring lazily evaluated statics. insert() each time? Dec 3, 2022 · You want . My thought process was that it would be nice to be able to look up an object by one of it's members while still maintaining the the collection by modifying the Vector. use std::collections::HashMap; We can import the HashMap module using the use declaration. In most situations, you will have some memory allocation available, so alloc is an option. May 31, 2020 · Hello, I'm learning Rust and I was trying to complete one of the excercise of The Book and the way I'm trying to resolve it is to use a HashMap<String, Vec>. symmetric_difference: get all the elements that are in one set or the other, but not both. Push to Vector in Hashmap. Convert the entire HashMap into an iterator and discard the keys: use std::collections::HashMap; fn only_values<K, V>(map: HashMap<K, V>) -> impl Iterator<Item = V> { map. May 7, 2017 · I want the vector with the same elements to hash to the same hash code. So instance would need to be dereferenced twice in order to access the element in inputs, which Oct 21, 2015 · How does one append to a vector that is a hashmap value? use std::collections::HashMap; fn main() { let mut dict = HashMap::new(); let mut prefix = ["", ""]; let lorem = "Lorem ipsum dolor sit amet, consectetur adipisicing elit. 3 HashMaps - Hash Maps - The Rust Programming Language Using a hash map and vectors, create a text interface to allow a user to add employee names to a department in a company. ” Then let the user retrieve a list of all people in a department or all Feb 4, 2024 · Struct std :: collections :: hash_map :: Values. Alternatively, BTreeMap is sorted based on the key. Thanks in advance. iter() Apr 18, 2017 · If the vector has one item and a capacity of one, adding another value to the vector will cause a re-allocation and copying of all the values in the vector, invalidating any references into the vector. vector; hash; rust; Share. In Rust, local variables are stored on the stack, which means that they have to have a fixed size, known at compile time. Correct answer at rustlings course, but Apr 16, 2023 · In the current implementation, iterating over map takes O (capacity) time instead of O (len) because it internally visits empty buckets too. I'm not sure what the best practice is in Rust for this. 0 · source ·. This is orthogonal to whether you use an Option. BTreeMap sorts its elements by key by default, therefore exchanging the place of your key and value and putting them into a BTreeMap. Please find below sample code: let mut queue : HashMap<Vec<u8>, Vec<u8>> = HashMap::new(); The last of our common collections is the hash map. rust; let mut scores = HashMap::new(); Mar 17, 2024 · An iterator that maps the values of iter with f. Step 2) vec. hybrid static + dynamic keys. max () {println! ("max: {}", max);} This returns the key with the highest value, not the key max associated value. Keys are unique no duplicates allowed in the key but the value can be duplicated. This would cause all of your keys in your index to point to arbitrary memory addresses, thus leading to unsafe behavior. clone(); Sep 26, 2020 · Step 1) Super fast hash key lookup --> returns vector bucket of values. As long as there is a memory allocator, it is possible to use serde_json without the rest of the Rust standard library. looking ahead. [ −] pub struct Values<'a, K: 'a, V: 'a> { /* private fields */ } Expand description. Eum debitis earum quidem dolorem quos consequatur perspiciatis architecto! Mar 23, 2018 · vector; hashmap; rust; Share. Once I add a value to that map I don't know how to retrieve the value ( Vec<String> ) as mutable to add another element to that Vec. Sep 20, 2021 · Rust interprets such map() invocation as intending to transform the iterator over words to an iterator over mutable references to their counts. With that, FnOnce will not be required. If you want the heap to own the values, you can Crate. insert (0, vec[i as usize][1]); } else {. HashMap is a hash table, searching for the String is an O (1) operation. If capacity is 0, the hash map will not allocate. name: String, power: usize, } A place for all things related to the Rust programming language—an open-source systems language that emphasizes performance, reliability, and productivity. Dec 6, 2021 · A Vec<Vec<u8>> for a 5x5 board has 6 heap allocations and a bit of storage on the stack for the outer vector. The "good" news is that Rust is being consistent about how references work when the thing being referenced moves. Mar 27, 2021 · I'm trying to merge a vector with &str slices into a HashMap but can't figure out why it doesn't work. enums as keys. let mut map = HashMap::new(); map. Oct 25, 2022 · 1 Answer. push(HashMap::new()); for row in 0. HashMap is part of the Rust standard collections library, so we must include the HashMap module in our program to use it. A HashMap contains a collection of indices, which we call keys, and a collection of values. Warning: hash_builder is normally randomly generated, and is designed to allow HashMaps to be resistant to attacks that Dec 27, 2020 · However, if you're building in a real no_std environment, you can use Vec provided you use the alloc crate, which allows you to allocate memory. Consider using the From trait. push(user); } In this Rust tutorial we learn how to create a hashmap, which is a collection of key:value pairs. for i in vec {. Rust Collect Hashmap from Iterator of Pairs. [ −] A wrapper around the std::collections::HashMap that uses case-insensitive Strings for keys. use BTreeMap for sorted data. map(|(k,v)| (v,k)). Now, we can create a hashmap using the new() method in the Jun 27, 2017 · 9. Sorted by: 15. insert(String::from("three"), 3); This includes built-in Rust standard library types like Vec<T> and HashMap<K, V>, as well as any structs or enums annotated with #[derive(Serialize)]. Version 2 Here we just get a vector of str Jul 25, 2021 · In Rust, AFAIK, we cannot move or reference vector elements. Jan 6, 2020 · I want to be able to convert this vector into a hash map in order to allow for quick access of each element. One solution is to keep track of the items you intend to remove in a Vec and then remove them afterwards: fn do_it(map: &mut HashMap<String, String>) {. map(|(_k, v)| v) } You can then do whatever you want with the iterator, including collecting it into a Vec<_>. Ideally I would like something like this: use std::collections::HashMap; fn main() { let mut map: HashMap<Vec<u8>, bool> = HashMap::new(); if map. HashMap keys can be booleans, integers, strings, or any other type that implements the Eq and Hash traits. Printing the addresses tends to confirm that guess (however the test is not I'm trying to find an efficient way to collect duplicates from a vector. iter() // . TL;DRRustでHashMapの中身のVecを変更するにはget_mut ()を使う.本題例えば,以下のようなHashMapを作成したとする.use std::collections::H. I did a benchmark in C a few years back in which a GLib GPtrArray was faster than a GHashTable up to around Mar 17, 2024 · where Self: Sized , F: FnMut (& [Self:: Item; N ]) -> R, 🔬This is a nightly-only experimental API. collect(); To expand the contents of the inner hash maps into the iterator, you can use flat_map: let vector_of_tuples: Vec<_> = items. The key type of the CaseInsensitiveHashMap is always UniCase<String> . Follow edited Mar 23, 2018 at 14:42. Aug 7, 2015 · I assumed Rust would know that counter would go out of scope once acc was returned. entry(word). You would then be free to do whatever you want with those references, perhaps collect them in a vector. Dec 14, 2016 · I can use vec![1,2,3] to build a vector. §Notes about side effects The map iterator implements DoubleEndedIterator, meaning that you can also map backwards: Mar 5, 2018 · I'm trying to build a HashMap with vectors as values and I have problems with borrowing / lifetimes. . How many empty slots there are will depend on your usage, if you have high peak usage however iterating over a now mostly empty HashMap will be quite slower than iterating over a Vec which is much more compact. Iterating over a HashMap will be slower, simply because the values are not as tightly packed in the HashMap: there are empty slots. If the number of elements is very small, and the keys are long (making the hash expensive) and key comparisons can mostly be decided quickly (because most keys have differences in their first bytes), then a Vec may be faster. The default hashing algorithm is currently AHash, though this is subject to change at any point in the future. let m = HashMap::from([. See its documentation for more. capacity. Aug 3, 2021 · I have the following HashMap:. How to get memory occupied by an object in rust from the code itself. This makes it possible to initialize concisely without needing to specify types or write macros. read_line(&mut buf) { Ok Mar 31, 2018 · This is ultimately fundamentally impossible. This is a vector containing both keys and values. lazy_static. In this case, you are moving the accumulator into an "output slot". iter() { users_by_level . Many programming languages support this kind of data structure, but they often use a different name, such as hash, map, object, hash table, dictionary, or associative array For example, a vector with capacity 10 and length 0 would be an empty vector with space for 10 more elements. This struct is created by the map method on Iterator. static strings as keys. Warning: hasher is normally randomly generated, and is designed to allow HashMaps to be resistant to attacks that cause many collisions and very poor performance. 0. The items in question are structs, and they count as duplicates when the name fields are equal. insert(String::from("one"), 1); map. Your construction requires the size of the value on the stack to be determined at runtime. @cafce25 is exactly right. iter() Dec 26, 2021 · Is there a way to consume a HashMap and get a vector of values in Rust? 5. 2 Answers. May 22, 2019 · I am trying to implement Karger's algorithm in Rust and I have run into an issue while trying to update a mutable hashmap in a while loop. The compiler prevents that. The next most natural value for ~str, I think, is ~"", that is, an empty string. use std::collections::HashMap; fn main() {. It works, but I feel like I'm struggling against the borrow-checker with the use of: an extra let tmp = binding to increase the lifetime of my temp value. Nov 3, 2021 · If not, is there an equally simple alternative that would perform better, by avoiding empty vector initialization for example (in case LLVM doesn't optimize that)? rust Share May 3, 2021 · let classes: HashMap(String, HashSet<String>) = HashMap::new() which is used to store students and whos classes. Setting it manually using this function can expose a DoS attack vector. insert( key, value); } The output of the example code is: Jan 16, 2021 · You can use collect () to build a vector from an iterator without an explicit loop: let vector_of_tuples: Vec<(u64, u64, bool)> = items. collect(); should give you a sorted map according to character frequency. collect(); These will then be referenced later in the library. insert (1, vec[i as usize][1]); = note: an as expression can only be used to convert between primitive types. My current idea is to use a hash map, where the keys are the name fields and the values are vectors containing references to the full structs. The map is updated successfully, but then in the next iteration when it was cloned, the values that were updated don't seem to have been changed. The vector can grow as long as the length is smaller than the capacity. or_insert(0) += 1; map } fold () takes two arguments: an initial value, and a closure with two arguments: an ‘accumulator’, and an element. Insertion In HashMap : The type HashMap<K, V> stores a mapping of keys of type K to values of type V using a hashing function, which determines how it places these keys and values into memory. 3: 10574: Nov 14, 2017 · HashMap::get returns an Option<&Type>, not an Option<Type>, which is why just returning the matched value fails to compile. Since this is a simple wrapper around the standard HashMap, please see its documentation for more information. hyousef January 18, 2020, 9:55am 1. Jun 23, 2020 · This code just does an unwrap, expecting that there would be at least one element. How to iterate through a HashMap<Vec<u8>,Vec<u8>> 1. entry(&user. We must also derive PartialEq , which is required if Eq is derived. This is understandable and relates to the non-lexical lifetimes discussion. uo vc ri jp ef dv rf gz zk kh
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