Hashmaps

Recipe	Crates
Hashmaps

HashMap is a key-value data structure. It allows you to store data in an unordered collection, where each element is identified by a unique key. This makes HashMap an excellent choice for lookups, insertions, and deletions based on keys.

All of the hashmap keys must have the same type as each other, and all of the values must have the same type.

use std::collections::HashMap;

fn main() {
    let mut scores = HashMap::new();

    scores.insert(String::from("Blue"), 10);

    // Update the value
    scores.insert(String::from("Blue"), 25);

    let team_name = String::from("Blue");
    // Get an Option<i32> rather than an Option<&i32>, then unwrap_or to
    // set score to zero if scores doesn't have an entry for the key.
    let _score = scores.get(&team_name).copied().unwrap_or(0);

    // Enumerate
    for (key, value) in &scores {
        println!("{key}: {value}");
    }

    // Adding a Key and Value only if a Key isn't present
    scores.entry(String::from("Yellow")).or_insert(50);
}

Related Data Structures

• B-trees.
• Other Maps.

Related Topics

• Concurrent Data Structures.
• Data Structures.
• Databases.
• Hashing.
• Key-Value Stores.