I have been using Darren’s Related Posts plugin (DRPP) for a long time. For my purposes it was the best plugin for showing related posts that I had encountered. After a while I decided that I was not completely satisfied with the way that it seemed to favor more recent posts. I developed a new algorithm that I felt would not give preference to newer posts unless they were actually more related.

When I learned that WordPress would be adding native tag support in version 2.3 I decided that I would create my plugin to work with tags after they arrived. Life got busy so I never worked on the plugin until version 2.5 came out (partly because I wanted to convert the post_meta “keywords” from DRPP to tags). I finally buckled down and created my Similarity plugin this week. I have tested it on version 2.3.3 and version 2.5 (I assume it will work with any version of 2.3). I will continue to test it on new versions of WordPress as they are made public. (Przeczytaj opis wtyczki po polsku)

Latest Version 2.13.1 (September 9, 2009)

New options make it possible to layout and style the php function generated lists (for sidebars) independent of the auto-generated list. – Version 2.13 was released with an incomplete development copy of the plugin so it did not have the promised functionality. (In other words, “Pay attention Miller.”)

To install it simply unzip the file linked above and save it in your plugins directory under wp-content. In the plugin manager activate the plugin. Settings for the plugin may be altered under the Similarity page of the Options menu (version 2.3) or Settings menu (version 2.5 or later).

Options include:

  • Number of posts to show – this is a maximum, it won’t invent connections that don’t exist, set it to 0 (or less) and it will display all matches.
  • Minimum match strength – enter a number between zero and one (one being a perfect match) and items related weaker than the number indicated will not be included – this limit is ignored for the one extra if that option is used.
  • Default Display if no matches – if there are no matches this is what will be displayed, this is not displayed if there are matches, but fewer than the set maximum.
  • Text and Codes before the list – assuming you want to do a list this is where you would place the <ul> or <ol> You may also place any other code you would like to have preceeding the list. (There are two boxes here – one for function calls in your template and one for auto-generated lists.)
  • Text and Codes after the list – this would be the place for </ul> or </ol> You may also place any other code you would like to have following the list.(There are two boxes here – one for function calls in your template and one for auto-generated lists.)
  • Output template – this would be where you place the <li> tags. (There are two boxes here – one for function calls in your template and one for auto-generated lists.) There are also 4 template tags you may use (in any configuration you can imagine) to define how the results are displayed
    • {link} – provides a link – equivelent to <a href=”{url}”>{title}</a>
    • {strength} – outputs the calculated degree of relatedness
    • {url} is the permalink for the related post
    • {title} is the title for the related post
  • Display format for similarity strength – Value displays the {strength} in a decimal format (0.873), Percent displays the {strength} in a percentage format (87.3%), Text displays {strength} as a word (Strong, Mild, Weak, and Tenuous are the defaults), and Visual displays a color block (Green for 100% fading to Yellow and then to Red for weak connections)
  • Relative mixing weights – these values determine the ratio given to the weight of tags vs categories when using the sim_by_mix function. Invalid ratios are treated as a 1 to 1 balance.
  • Custom text for strength – allows you to insert custom text (including markup) for the strength indicator when using the text display format. (Hint: using markup allows for the possibility of showing custom images.)
  • Show one more random related post – dig deeper into the related post list with one random selection (you can set a minimum strength for these random items).
  • Auto-display a Similarity list at the end of a single post – without modifying any templates.

The plugin allows for three function calls anywhere in your page templates or their shortcodes in text widgets (all use the same options):

  • <?php sim_by_tag(); ?> – determines similarity based on the tags applied to the posts (shortcode: SIM-BY-TAG)
  • <?php sim_by_cat(); ?> – determines similarity based on the categories assigned to the posts (shortcode: SIM-BY-CAT)
  • <?php sim_by_mix(); ?> – determines similarity based on the tags and the categories with the relative weights determined by the relative mixing weights setting (shortcode: SIM-BY-MIX)

Alternately you may choose to auto-display any of the similarity lists at the end of posts on single-post pages without getting into the php by selecting the function you wish to auto-display on the Similarity options page.

About David

David is the father of 8 extremely organized children (4 girls / 4 boys) who is constantly seeking answers to tough questions related to parenting, education and politics while moonlighting for 40 hours each week as a technology professional. He also enjoys cooking, gardening, and sports.
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169 Responses to Similarity

  1. Tux28 says:

    Thanks a lot for this plugin ! it works great !
    Good job !

  2. Li-An says:

    it seems the plugin shows pages in relative posts in WP 3.0
    See here by example:
    The first relative link is the About page.

  3. Ulrich SOSSOU says:

    The plugin was not displaying sub pages (only parent ones). WP 2.9
    So I had to comment out this code (line 658) :
    if ($wp_version > 2.5) {
    $query .= ” and post_parent = 0″;

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