title: Is there a way to apply a UDF function returning multiple values in Rust polars?
body: <p>I'm trying to use polars to apply a function from another library across each row of an input. I can't find any examples or tests of using an Expr to apply a function, even when it has one return value; so I'm lost.</p>
  <p>It's taking an input dataframe with two float columns, and trying to append three columns as generated by a function with this form:</p>
  <pre><code>fn f(a: f64, b: f64) -&gt; (f64, f64, f64);
  </code></pre>
  <p>Is there a simple way to do this?</p>