NOTE! Assigning the parser using a class name was added in version 2.0.11 (it is not part of the original plugin).

Demo

Name
Major
Gender
English
Japanese
Calculus
Overall grades
Student01 Languages male 80 70 75 medium
Student02 Mathematics male 90 88 100 good
Student03 Languages female 85 95 80 good
Student04 Languages male 20 50 65 bad
Student05 Mathematics female 70 78 70 medium
Student06 Mathematics male 44 65 60 bad

Javascript

// add parser through the tablesorter addParser method
$.tablesorter.addParser({
  // set a unique id
  id: 'grades',
  is: function(s) {
    // return false so this parser is not auto detected
    return false;
  },
  format: function(s, table, cell, cellIndex) {
    // format your data for normalization
    return s.toLowerCase()
      .replace(/good/,2)
      .replace(/medium/,1)
      .replace(/bad/,0);
  },
  // set type, either numeric or text
  type: 'numeric'
});

$(function() {
  $("table").tablesorter({
    theme: 'blue'
    // "sorter-grades" added as a class name in the HTML (new in v2.0.11)
    // or un-comment out the option below
    // ,headers: { 6: { sorter: 'grades' } }
  });

});

HTML

<table class="tablesorter">
  <thead>
    <tr>
      <th class="sorter-text">Name</th>
      <th>Major</th>
      <th>Gender</th>
      <th>English</th>
      <th>Japanese</th>
      <th>Calculus</th>
      <th class="sorter-grades">Overall grades</th> <!-- set the column parser using a class name -->
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>Student01</td>
      <td>Languages</td>
      <td>male</td>
      <td>80</td>
      <td>70</td>
      <td>75</td>
      <td>medium</td>
    </tr>
    <tr>
      <td>Student02</td>
      <td>Mathematics</td>
      <td>male</td>
      <td>90</td>
      <td>88</td>
      <td>100</td>
      <td>good</td>
    </tr>
    <tr>
      <td>Student03</td>
      <td>Languages</td>
      <td>female</td>
      <td>85</td>
      <td>95</td>
      <td>80</td>
      <td>good</td>
    </tr>
    <tr>
      <td>Student04</td>
      <td>Languages</td>
      <td>male</td>
      <td>20</td>
      <td>50</td>
      <td>65</td>
      <td>bad</td>
    </tr>
    <tr>
      <td>Student05</td>
      <td>Mathematics</td>
      <td>female</td>
      <td>70</td>
      <td>78</td>
      <td>70</td>
      <td>medium</td>
    </tr>
    <tr>
      <td>Student06</td>
      <td>Mathematics</td>
      <td>male</td>
      <td>44</td>
      <td>65</td>
      <td>60</td>
      <td>bad</td>
    </tr>
  </tbody>
</table>
Next up: Writing custom parsers, advanced ››