main.rs

use std::fs::File;
use std::io::{BufRead, BufReader};
use rayon::iter::{ParallelBridge};
use serde::Deserialize;
use rayon::iter::ParallelIterator;

#[derive(Deserialize, Debug)]
struct Business {
    stars: f64,
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let f = File::open("/home/sumeet/Downloads/yelp_dataset/yelp_academic_dataset_business.json")?;
    let bufreader = BufReader::new(f);
    let (len, sum) = bufreader.lines().par_bridge().map(|line| {
        let b : Business = serde_json::from_str(line.as_ref().unwrap()).unwrap();
        (1, b.stars)
    }).reduce(||(0, 0.), |(acc_ct, acc_rating), (ct, rating)| {
        (acc_ct + ct, acc_rating + rating)
    });
    dbg!(sum / len as f64);

    Ok(())
}

// > time target/debug/yelp
// [src/main.rs:21] sum / len as f64 = 3.5967235576603303
//
// ________________________________________________________
// Executed in  879.57 millis    fish           external
//    usr time  855.58 millis  642.00 micros  854.93 millis
//    sys time   23.54 millis  255.00 micros   23.28 millis

// > time target/release/yelp
// [src/main.rs:21] sum / len as f64 = 3.5967235576603303
//
// ________________________________________________________
// Executed in  140.42 millis    fish           external
//    usr time  120.25 millis  701.00 micros  119.55 millis
//    sys time   20.15 millis  223.00 micros   19.93 millis


// fn old_main() {
//     let f = File::open("/home/sumeet/Downloads/yelp_dataset/yelp_academic_dataset_business.json")?;
//     let bufreader = BufReader::new(f);
//     let mut len = 0;
//     let mut sum = 0.;
//     for line in bufreader.lines() {
//         let line = line?;
//         let b: Business = serde_json::from_str(&line)?;
//         len += 1;
//         sum += b.stars;
//     }
//     dbg!(sum / len as f64);
//
// }