Rust Book - Section 8 Mean Median Mode

main.rs

use std::collections::HashMap;
use std::cmp::Ordering;

fn main() {
    // mean
    let v = vec![1.0, 2.0, 3.0, 4.0, 5.0];
    let empty_vector: Vec<f32> = Vec::new();
    let negative_vector = vec![-1.0, -15.0, -30.0, -55.0];
    let decimal_vector = vec![1.0, 2.0];

    println!("Mean is {}", mean(&v));
    println!("Mean of empty vector is {}", mean(&empty_vector));
    println!("Mean of negative vector is {}", mean(&negative_vector));
    println!("Mean of decimal vector is {}", mean(&decimal_vector));
    // can still use vector
    println!("first value of vector is : {}", v[0]);

    let v_odd = vec![5.0, 1.0, 2.0, 3.0, 4.0];
    let v_even = vec![6.0, 1.0, 2.0, 3.0, 4.0, 5.0];
    println!("Median of odd = {} (expected 3)", median(&v_odd));
    println!("Median of even = {} (expected 3.5)", median(&v_even));
    // can still use vector
    // original vector not sorted
    println!("first value of (now sorted) vector is : {}", v_odd[0]);

    let v = vec![1, 2, 2, 4, 4, 4, 4, 5];
    println!("Mode of {} (expected 4)", mode(&v));
}

fn mean(v: &Vec<f32>) -> f32 {

    let sum: f32 = v.iter().sum();

    let vector_length = v.len();
    match vector_length {
        0 => 0f32,
        _ => sum / vector_length as f32,
    }
}

fn median(v1: &Vec<f32>) -> f32 {

    // create a clone vector to not alter original vector
    let mut v = v1.clone();
    // https://doc.rust-lang.org/std/vec/struct.Vec.html#method.sort_by
    v.sort_by(|a, b| a.partial_cmp(b).unwrap());

    // select median
    let remain = v.len() % 2;
    let middle = v.len() / 2;

    match remain {
        0 => mean(&vec![v[middle-1], v[middle]]),
        _ => v[middle],
    }

}

fn mode(v: &Vec<i32>) -> i32 {
    let mut max = 0;
    let mut mode = 0;
    let mut counter_map: HashMap<i32, i32> = HashMap::new();

    for &i in v {
        let count = counter_map.entry(i).or_insert(0);
        *count += 1;

        match max.cmp(&count) {
            Ordering::Less => {
                max = *count;
                mode = i;
            },
            _ => (),
        }
    }

    mode
}