rust-ngram-nice.rs

extern crate csv;

use std::collections::HashMap;
use std::error;
use std::result;
use std::path::Path;
use std::process;

type Result<T> = result::Result<T, Box<error::Error>>;

fn process_file<P: AsRef<Path>>(path: P) -> Result<(u64, u64)> {
    let mut sum_by_key = HashMap::new();
    let mut rdr = csv::ReaderBuilder::new()
        .has_headers(false)
        .delimiter(b'\t')
        .from_path(path)?;

    let mut record = csv::StringRecord::new();
    while rdr.read_record(&mut record)? {
        let year = record[1].parse()?;
        let count = record[2].parse()?;
        *sum_by_key.entry(year).or_insert(0) += count;
    }
    match sum_by_key.iter().max_by_key(|&(_, &v)| v) {
        Some((&k, &v)) => Ok((k, v)),
        None => Err(format!("no records").into()),
    }
}

fn try_main() -> Result<()> {
    let (k, v) = process_file("/tmp/ngrams.tsv")?;
    if k != 2006 || v != 22569013 {
        Err(format!("bad result {:?} | {:?}", k, v).into())
    } else {
        Ok(())
    }
}

fn main() {
    if let Err(err) = try_main() {
        println!("{}", err);
        process::exit(1);
    }
}