top20.rs

/**
 * Prints top 20 words used in a file
 */
use std::cmp::min;
use std::collections::HashMap;
use std::env;
use std::fs;
use std::io;
use std::io::{BufRead, BufReader, Read};

fn main() {
    let arg: Vec<String> = env::args().collect();

    if arg.len() > 1 {
        for filename in &arg[1..] {
            let file = fs::File::open(filename)
                .expect(format!("Error reading content from file {}", filename).as_str());
            top_words(file, filename);
        }
    } else {
        top_words(io::stdin().lock(), "/dev/stdin");
    }
}

fn top_words(reader: impl Read, filename: &str) {
    let mut word_count: HashMap<String, u32> = HashMap::new();

    let buf_read = BufReader::new(reader);

    // Split contents of file into words and count them

    for line in buf_read.lines() {
        for word in line.unwrap().to_lowercase().split_whitespace() {
            *word_count.entry(word.to_owned()).or_insert(0u32) += 1;
        }
    }

    // Sort most frequent words
    let mut word_list: Vec<_> = word_count.iter().collect();
    word_list.sort_by(|a, b| b.1.cmp(a.1));
    let n = min(word_list.len(), 20);

    println!("{}:", filename);
    for f in &word_list[..n] {
        println!("{}\t{}", f.0, f.1);
    }
}