main.rs

extern crate csv;

use std::error::Error;
use std::collections::HashMap;
use csv::ReaderBuilder;

fn main() {
    match run() {
        Ok(_) => {},
        Err(e) => println!("Error: {:?}", e),
    };
}

fn run() -> Result<(), Box<Error>> {
    let mut map: HashMap<String, i64> = HashMap::new();
    let mut reader = ReaderBuilder::new()
        .delimiter(b'\t')
        .from_path("./googledata")?;

    for record in reader.records() {
        let record = record?;
        *map.entry(record[1].into()).or_insert(0) += record[2].parse()?;
    }

    if let Some((max_key, max_val)) = map.iter().max_by_key(|&(_, v)| v) {
        println!("max_key: {} sum: {}", max_key, max_val);
    } else {
        println!("No entries");
    }

    Ok(())
}