title: I need to change the Month column to date format
body: <p>My data set is monthly from Jan 1997 to Dec 2021. I need the month code to be in the correct format, however as.date doesn't recognise the cell contents as they are. Please help.</p>
  <pre><code> Month BrentSpot     GDP Agriculture Production Construction Services
  1 Jan-1997     23.54 63.8229     53.5614    81.9963      87.2775  59.4453
  2 Feb-1997     20.85 64.7182     53.9091    82.1917      87.8350  60.5018
  3 Mar-1997     19.13 64.9264     54.2569    81.6142      88.6714  60.8375
  4 Apr-1997     17.56 65.2327     55.1264    82.0006      89.5170  61.0981
  5 May-1997     19.02 64.7336     55.8220    82.0093      89.8144  60.4470
  6 Jun-1997     17.58 65.1322     56.3438    82.3350      89.4891  60.8886
  </code></pre>