title: Combine different values of multiple columns into one column in Polars
body: <p>I have the following Python Code with pandas</p>
  <pre><code>df['EVENT_DATE'] = df.apply(
          lambda row: datetime.date(year=row.iyear, month=row.imonth, day=row.iday).strftime(&quot;%Y-%m-%d&quot;), axis=1)
  </code></pre>
  <p>and want to transform it into a valid Polars Code. Does anyone have any idea to solve this?</p>