Cookbooks
Rust
Chapter 10. Data Formats and Serialization
Working with CSV

Rust:
Working with CSV

How to:

Rust, with its focus on safety and performance, offers excellent crates (libraries) for dealing with CSV files, with csv being the most popular. You’ll also need serde for serializing and deserializing data.

First, add the dependencies to your Cargo.toml:

[dependencies]
csv = "1.1"
serde = { version = "1.0", features = ["derive"] }

Reading CSV

To read a CSV file, define a struct that represents your data and derive Deserialize from serde:

use serde::Deserialize;
use std::error::Error;
use std::fs::File;
use std::io;
use std::process;

#[derive(Debug, Deserialize)]
struct Record {
    city: String,
    state: String,
    population: u64,
}

fn read_from_csv(file_path: &str) -> Result<(), Box<dyn Error>> {
    let file = File::open(file_path)?;
    let mut rdr = csv::Reader::from_reader(file);

    for result in rdr.deserialize() {
        let record: Record = result?;
        println!("{:?}", record);
    }
    Ok(())
}

fn main() {
    if let Err(err) = read_from_csv("cities.csv") {
        println!("error running example: {}", err);
        process::exit(1);
    }
}

Sample output for a CSV with city information might look like:

Record { city: "Seattle", state: "WA", population: 744955 }
Record { city: "New York", state: "NY", population: 8336817 }

Writing to CSV

To write to a CSV file, define a struct and derive Serialize:

use serde::Serialize;
use std::error::Error;
use std::fs::File;

#[derive(Serialize)]
struct Record {
    city: String,
    state: String,
    population: u64,
}

fn write_to_csv(file_path: &str, records: Vec<Record>) -> Result<(), Box<dyn Error>> {
    let file = File::create(file_path)?;
    let mut wtr = csv::Writer::from_writer(file);

    for record in records {
        wtr.serialize(&record)?;
    }
    wtr.flush()?;
    Ok(())
}

fn main() -> Result<(), Box<dyn Error>> {
    let records = vec![
        Record {
            city: "Los Angeles".into(),
            state: "CA".into(),
            population: 3979563,
        },
        Record {
            city: "Chicago".into(),
            state: "IL".into(),
            population: 2695598,
        },
    ];

    write_to_csv("output.csv", records)?;

    Ok(())
}

This will create output.csv with the data:

city,state,population
Los Angeles,CA,3979563
Chicago,IL,2695598

By leveraging Rust’s powerful type system and the ecosystem’s robust crates, working with CSV data becomes both efficient and straightforward, ensuring safety and performance in your data processing tasks.

Working with JSON