word count

Cargo.toml

[package]
name = "wc"
version = "0.1.0"
edition = "2018"

[dependencies]
regex = "1"
lazy_static = "1"

main.rs

use std::collections::HashMap;
use std::fs;
use std::io::{self, BufRead};
use regex::Regex;

lazy_static::lazy_static! {
    static ref WORD_REGEX: Regex = Regex::new(r"(?i)[a-z]{2,}").unwrap();
    static ref FNAME_REGEX: Regex = Regex::new(r"(?i)\.txt$").unwrap();
}

fn main() -> io::Result<()> {
    let mut word_counts = HashMap::new();

    for path in fs::read_dir(".")?
        .filter_map(|p| p.ok())
        .map(|p| p.path())
        .filter(|p| p.is_file() && FNAME_REGEX.is_match(&p.to_string_lossy())) {

            let file = fs::File::open(path)?;
            for line in io::BufReader::new(file).lines() {
                for cap in WORD_REGEX.captures_iter(&line?) {
                    *word_counts.entry(cap[0].to_string()).or_insert(0) += 1u32;
                }
            }
        }

    let mut word_array: Vec<(String, u32)> = word_counts.into_iter().collect();
    word_array.sort_by(|a, b| b.1.partial_cmp(&a.1).unwrap());
    let final_size =  std::cmp::min(word_array.len(), 10);
    for entry in &word_array[..final_size] {
        println!("{} {}", entry.1, entry.0);
    }

    Ok(())
}