JSFiddle - React, Tailwind, and code Playground

HTML

<table id="test" border="1">
    <tr>
        <td>test1</td>
        <td>test2</td>
        <td>test3</td>
    </tr>
      <tr>
          <td>test4</td>
          <td>test2</td>
          <td>test5</td>
    </tr>
    <tr>
        <td>test6</td>
        <td>test2</td>
        <td>test9</td>
    </tr>
          <tr>
              <td>test6</td>
              <td>test8</td>
              <td>test9</td>
    </tr>
          <tr>
              <td>test9</td>
              <td>test6</td>
              <td>test2</td>
    </tr>
    <tr><td colspan="3"><button id="removeDupes">Remove Dupes</button> </td></tr>
</table>

JavaScript

var seen = {};
$('#removeDupes').on('click', function(){
    $('#test tr td').each(function() {
        var txt = $(this).text();
        var index = $(this).parent('tr').children('td').index(this);
        if (!seen[index]){
            seen[index] = new Array();
        }
        
        if (seen[index][txt]) {
            $(this).html('&nbsp;');
        }
        else {
            seen[index][txt] = true;
        }
    });
});