POLARS Dataframe innerJOIN in RUST

Question

RUST / POLARS nooby question :)

I can not get the "inner_join" to work:

use polars::prelude::*;
use std::fs::File;
use std::path::PathBuf;
use std::env;

fn main() -> std::io::Result<()> {

    let mut root = env::current_dir().unwrap();
    let file_1 = root.join("data_1.csv");
    let file_2 = root.join("data_2.csv");

    // Get data from first file (one column data: column_1)
    let file = File::open(file_1).expect("Cannot open file.");
    let first_data = CsvReader::new(file)
        .has_header(false)
        .finish()
        .unwrap();

    // WORKS !
    println!("{}", first_data);

    // Get data from second file (one column data: column_1)
    let file = File::open(file_2).expect("Cannot open file.");
    let second_data = CsvReader::new(file)
        .has_header(false)
        .finish()
        .unwrap();

    // WORKS !
    println!("{}", second_data);

    // Trying to get an INNER join
    let all_data = first_data.inner_join(second_data, "column_1", "column_1");

    println!("{}", all_data);

    Ok(())
}

BUILD OUTPUT:

error[E0277]: `&str` is not an iterator
   --> src\main.rs:33:31
    |
33  |     let all_data = first_data.inner_join(second_data, "column_1", "column_1");
    |                               ^^^^^^^^^^ `&str` is not an iterator; try calling `.chars()` or `.bytes()`
    |
    = help: the trait `Iterator` is not implemented for `&str`
    = note: required because of the requirements on the impl of `IntoIterator` for `&str`
note: required by a bound in `hash_join::<impl DataFrame>::inner_join`
   --> C:\Users\rnio\.cargo\registry\src\github.com-1ecc6299db9ec823\polars-core-0.23.1\src\frame\hash_join\mod.rs:645:12
    |
645 |         I: IntoIterator<Item = S>,
    |            ^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `hash_join::<impl DataFrame>::inner_join`

Looking for any hint / information what I am missing ... I looked at POLARS Features ... and could not see a flag needed to do JOIN operations ... any ideas ?

Thanks in advance :)

Answer 1

The problem is with the columns, not with the DataFrame.

The inner_join function takes in the DataFrame and two sets of columns that implement IntoIterator. Because you are passing in strings for the column names, it's giving you the error telling you to call .chars() to turn it into an iterator over the characters.

You should be able to get this to work with the following:

let all_data = first_data.inner_join(&second_data, ["column_1"], ["column_1"]);

You can see the definition of this function here: https://docs.rs/polars/latest/polars/frame/struct.DataFrame.html#method.inner_join