rustHow to create a HashMap of HashMaps in Rust?

A HashMap of HashMaps can be created in Rust using the HashMap::new() method. The following example code creates a HashMap of HashMaps with String keys and i32 values:

use std::collections::HashMap;

let mut map_of_maps: HashMap<String, HashMap<String, i32>> = HashMap::new();

let mut inner_map1: HashMap<String, i32> = HashMap::new();
inner_map1.insert(String::from("key1"), 1);
inner_map1.insert(String::from("key2"), 2);

let mut inner_map2: HashMap<String, i32> = HashMap::new();
inner_map2.insert(String::from("key3"), 3);
inner_map2.insert(String::from("key4"), 4);

map_of_maps.insert(String::from("map1"), inner_map1);
map_of_maps.insert(String::from("map2"), inner_map2);

println!("{:?}", map_of_maps);

Output example

{"map1": {"key1": 1, "key2": 2}, "map2": {"key3": 3, "key4": 4}}

Code explanation

1. use std::collections::HashMap; - imports the HashMap type from the std::collections module.

2. let mut map_of_maps: HashMap<String, HashMap<String, i32>> = HashMap::new(); - creates a HashMap with String keys and HashMap values, where the HashMap values have String keys and i32 values.

3. let mut inner_map1: HashMap<String, i32> = HashMap::new(); - creates a HashMap with String keys and i32 values.

4. inner_map1.insert(String::from("key1"), 1); - inserts a key-value pair into the inner_map1 HashMap.

5. map_of_maps.insert(String::from("map1"), inner_map1); - inserts a key-value pair into the map_of_maps HashMap, where the value is the inner_map1 HashMap.

Helpful links

• Rust HashMap Documentation

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