Get a list of data and count the number of repeating groups and display the most frequent

count_data_frequency.rs

use std::collections::{BTreeMap, HashMap};

fn main() {
    let frequency = [19, 19, 20, 32, 35, 19, 32];

    // use hashmap to store k/v pairs
    let mut seek_hash: HashMap<i32, u8> = HashMap::new();
    let mut seek_hash_sorted: BTreeMap<i32, u8> = BTreeMap::new();
    let mut highest_freq_val = 0;
    let mut highest_freq_key = 0;

    for num in frequency {
        // check if key in hash map
        match seek_hash.contains_key(&num) {
            false => {
                if num > 0 {
                    seek_hash.insert(num, 1);
                }
            }
            true => {
                // update existing value by hash key
                *seek_hash.entry(num).or_default() += 1;
            }
        }
    }

    // insert into Btree map
    // borrow (immut) from previous owner
    let updated_hashmap = &seek_hash;
    for (key, value) in updated_hashmap {
        if value > &highest_freq_val {
            highest_freq_val = *value;
            highest_freq_key = *key;
        }
      
        // use a * to dereference the borrow
        seek_hash_sorted.insert(*key, *value);
    }

    println!(
        "most occurring number is: {} with {} occurrences",
        highest_freq_key, highest_freq_val
    );
}