With scoped threads

main.rs

use std::collections::HashMap;

fn main() -> Result<(), String> {
    let numbers = vec![1, 2, 3, 4, 5, 6];

    // This creates the scope for the threads
    let (median, mode) = std::thread::scope(|scope| {
  
        // This scoped thread calculates average
        let median_thread = 
            scope.spawn(|| numbers.iter().sum::<i32>() as f32 / numbers.len() as f32);

        // This scoped thread calculates mode
        let mode_thread = scope.spawn(|| {
            let mut counter = HashMap::new();
            for value in numbers.iter() {
                *counter.entry(value).or_insert(0) += 1;
            }

            counter.into_iter()
                .max_by_key(|&(_, count)| count)
                .map(|(val, _)| val)
        });

        (median_thread.join(), mode_thread.join())
    });

    let (median, mode) = match (median, mode) {
        (Ok(median), Ok(Some(mode))) => Ok((median, mode)),
        _ => Err("Calculations have failed".to_string()),
    }?;

    println!("For the vector {numbers:?} the median is {median} and the mode is {mode}");
    Ok(())
}