Craft: Add entry author's category field to entry listing

gistfile1.php

public function modifyEntryTableAttributes( &$attributes, $source ) {
  // Note: the number "3" is the relevant section's ID
  if ($source == 'section:3')
  {
      // Add a dummy field key – this could be called anything but avoid conflicts
      $attributes['myEntryAuthorCategory'] = Craft::t('Author category');
  }
}

public function getEntryTableAttributeHtml(EntryModel $entry, $attribute)
{
  if ($attribute == 'myEntryAuthorCategory')
  {
      // Get entry author
      $author = craft()->users->getUserById($entry->authorId);
      // Get category field for author – "categoryFieldHandle" represents the handle for your category field
      if ($categories = $author->categoryFieldHandle->find())
      {
          $temp = array();
          // Build HTML output (category titles/links)
          foreach ($categories as $category)
          {
              $attributeHtml = $category->title;
              if ( $category->cpEditUrl ) {
                  $attributeHtml = '<a href="' . $category->cpEditUrl . '">' . $attributeHtml . '</a>';
              }
                  $temp[] = $attributeHtml;
              }
              return ! empty( $temp ) ? implode( ', ', $temp ) : false;
      }
      return false;
  }
}