title: Create array of columns letters where column header fulfills criteria
body: <p>in Google Sheets using formulars I would like to build an array of the columns that fulfills a simple criteria, so for example:</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>A</th>
  <th>B</th>
  <th>C</th>
  <th>D</th>
  <th>E</th>
  <th>F</th>
  <th>G</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>h1</td>
  <td>h2</td>
  <td>h2</td>
  <td>h1</td>
  <td>h3</td>
  <td>h2</td>
  <td>h1</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>Then I would like to have the array {A:A,D:D,G:G} if I search for 'h1'</p>