Iterate over vector and push to a hashmap vector value in rust?

I have this vector of users and i want to transform it into hashmap with key as level of user (which is a string) and value as a vector of users

#[derive(Debug, Serialize, Deserialize)]
pub struct User {
    pub id: String,
    pub email: String,
    pub first_name: String,
    pub last_name: String,
    pub level: String,
}

let users: Vec<User> = serde_json::from_str(&data).unwrap();
let mut users_by_level: HashMap<String, Vec<User>> = HashMap::new();

for user in users.iter() {
    users_by_level
        .entry(user.level.clone())
        .or_insert(Vec::new())
        .push(user);
}

But i'm getting this error mismatched types expected 'User', found '&User'

Can anyone help me with this? i'm new to rust

iter produces an iterator of references. This is useful if you keep the Vec around, especially since you don't need to clone the key.

let mut users_by_level: HashMap<&str, Vec<&User>> = HashMap::new();

for user in users.iter() {
    users_by_level
        .entry(&user.level)
        .or_insert(Vec::new())
        .push(user);
}

If you want to transfer ownership to the HashMap, like when you don't need the Vec or you want to mutate the items, you can use into_iter.

let mut users_by_level: HashMap<String, Vec<User>> = HashMap::new();

for user in users.into_iter() {
    users_by_level
        .entry(user.level.clone())
        .or_insert(Vec::new())
        .push(user);
}

For loops call into_iter automatically, so you can simply pass users directly to get the same thing.

for user in users {

The reason why its giving you a mismatch type error is that when you are iteration through a collection like a Vec, you are given a borrow to the data within the collection. In this case since you are iterating through the users vector, the individual entry within the for loop is a borrow of type User &User, therefore you should attempt to clone the user that is being iterated when you insert it within the HashHap, like so:

use serde::{Deserialize, Serialize};
use std::collections::HashMap;
#[derive(Debug, Serialize, Deserialize, Clone)]
pub struct User {
    pub id: String,
    pub email: String,
    pub first_name: String,
    pub last_name: String,
    pub level: String,
}

fn main() {
    let users: Vec<User> = serde_json::from_str(&data).unwrap();
    let mut users_by_level: HashMap<String, Vec<User>> = HashMap::new();

    for user in users.iter() {
        users_by_level
            .entry(user.level.clone())
            .or_insert(Vec::new())
            .push(user.clone());
    }
}

The user struct can derive the clone trait since it is made up of types that can be cloned (in this case owned Strings). Then in the for loop when you insert user as the value, you use the .clone() method to copy the user to mutable HashMap.