Count words

playground.rs

use std::collections::HashMap;

fn count_words(text: &str) -> HashMap<&str, usize> {
    text.split(' ').fold(
        HashMap::new(),
        |mut map, word| { *map.entry(word).or_insert(0) += 1; map }
    )
}

#[test]
fn test1() {
    let counts = count_words("lorem lorem ipsum");

    assert_eq!(counts["lorem"], 2);
    assert_eq!(counts["ipsum"], 1);
    assert_eq!(counts.get("non-existing-word"), None);
}