การนับและการจัดกลุ่ม

use std::collections::HashMap;

fn main() {
    let mut counts = HashMap::new();
    for n in [1, 1, 2, 3, 3, 3] {
        *counts.entry(n).or_insert(0) += 1;
    }
    println!("threes: {}", counts[&3]);
}

use std::collections::HashMap;

fn main() {
    let mut freq = HashMap::new();
    for c in "banana".chars() {
        *freq.entry(c).or_insert(0) += 1;
    }
    println!("a: {}, n: {}", freq[&'a'], freq[&'n']);
}

use std::collections::HashMap;

fn main() {
    let text = "go go stop go";
    let mut counts = HashMap::new();
    for w in text.split_whitespace() {
        *counts.entry(w).or_insert(0) += 1;
    }
    println!("go: {}", counts["go"]);
}

use std::collections::HashMap;

fn main() {
    let mut counts = HashMap::new();
    for c in "aabbbc".chars() {
        *counts.entry(c).or_insert(0) += 1;
    }
    let top = counts.iter().max_by_key(|(_, &v)| v).unwrap();
    println!("most common: {}", top.0);
}

use std::collections::HashMap;

fn main() {
    let mut groups: HashMap<bool, Vec<i32>> = HashMap::new();
    for n in 1..=6 {
        groups.entry(n % 2 == 0).or_default().push(n);
    }
    println!("evens: {:?}", groups[&true]);
}

use std::collections::HashMap;

fn main() {
    let words = ["apple", "avocado", "banana"];
    let mut by_letter: HashMap<char, Vec<&str>> = HashMap::new();
    for w in words {
        let first = w.chars().next().unwrap();
        by_letter.entry(first).or_default().push(w);
    }
    println!("a-words: {}", by_letter[&'a'].len());
}

use std::collections::HashMap;

fn main() {
    let words = ["hi", "yo", "hey", "hello"];
    let mut by_len: HashMap<usize, Vec<&str>> = HashMap::new();
    for w in words {
        by_len.entry(w.len()).or_default().push(w);
    }
    println!("len 2: {}", by_len[&2].len());
}

use std::collections::HashSet;

fn main() {
    let visits = ["sam", "mia", "sam", "leo", "mia"];
    let unique: HashSet<&str> = visits.iter().copied().collect();
    println!("unique visitors: {}", unique.len());
}

use std::collections::HashMap;

fn main() {
    let mut counts = HashMap::new();
    for c in "abca".chars() {
        *counts.entry(c).or_insert(0) += 1;
    }
    let mut keys: Vec<_> = counts.keys().collect();
    keys.sort();
    for k in keys {
        println!("{}: {}", k, counts[k]);
    }
}

use std::collections::HashMap;

fn main() {
    let sales = [("a", 10), ("b", 5), ("a", 3)];
    let mut totals: HashMap<&str, i32> = HashMap::new();
    for (k, amount) in sales {
        *totals.entry(k).or_insert(0) += amount;
    }
    println!("a total: {}", totals["a"]);
}