title: POLARS Dataframe innerJOIN in RUST
body: <p>RUST / POLARS nooby question :)</p>
  <p>I can not get the &quot;inner_join&quot; to work:</p>
  <pre><code>use polars::prelude::*;
  use std::fs::File;
  use std::path::PathBuf;
  use std::env;
  
  fn main() -&gt; std::io::Result&lt;()&gt; {
  
      let mut root = env::current_dir().unwrap();
      let file_1 = root.join(&quot;data_1.csv&quot;);
      let file_2 = root.join(&quot;data_2.csv&quot;);
  
      // Get data from first file (one column data: column_1)
      let file = File::open(file_1).expect(&quot;Cannot open file.&quot;);
      let first_data = CsvReader::new(file)
          .has_header(false)
          .finish()
          .unwrap();
  
      // WORKS !
      println!(&quot;{}&quot;, first_data);
  
      // Get data from second file (one column data: column_1)
      let file = File::open(file_2).expect(&quot;Cannot open file.&quot;);
      let second_data = CsvReader::new(file)
          .has_header(false)
          .finish()
          .unwrap();
  
      // WORKS !
      println!(&quot;{}&quot;, second_data);
  
      // Trying to get an INNER join
      let all_data = first_data.inner_join(second_data, &quot;column_1&quot;, &quot;column_1&quot;);
  
      println!(&quot;{}&quot;, all_data);
  
      Ok(())
  }
  
  </code></pre>
  <p>BUILD OUTPUT:</p>
  <pre><code>error[E0277]: `&amp;str` is not an iterator
     --&gt; src\main.rs:33:31
      |
  33  |     let all_data = first_data.inner_join(second_data, &quot;column_1&quot;, &quot;column_1&quot;);
      |                               ^^^^^^^^^^ `&amp;str` is not an iterator; try calling `.chars()` or `.bytes()`
      |
      = help: the trait `Iterator` is not implemented for `&amp;str`
      = note: required because of the requirements on the impl of `IntoIterator` for `&amp;str`
  note: required by a bound in `hash_join::&lt;impl DataFrame&gt;::inner_join`
     --&gt; 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&lt;Item = S&gt;,
      |            ^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `hash_join::&lt;impl DataFrame&gt;::inner_join`
  </code></pre>
  <p>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 ?</p>
  <p>Thanks in advance :)</p>