Example settings on a User Name field.

INTRODUCTION

Relationships or other joins in Views often create "duplicate" results. For example, a node with a field that has multiple values may show up in the View once per value in the multi-value field. It's frustrating, and the "DISTINCT" SQL query option in the Views UI does not actually solve the problem because the result row is technically distinct. This module aims to give a simple GUI method to remove or aggregate these "duplicate" rows.

For any given field, including "Global: Text" fields, you can optionally mark the field as filtered ("Filter Repeats") or aggregated ("Aggregate Repeats"). All rows with the same value in that field will either be removed as duplicates (filtered), or aggregated in-line.

The "value" of the field as used for filtering or aggregation can be taken pre-render (fastest and totally cacheable), or post-render (after any rewrite rules or other transformations have occurred). Post-render actions are a bit slower (the View must be re-rendered, though the query is not re-run), but also work with Global fields, like Global: Text w/rewrite rules.

EXAMPLES

Consider a Course node with multiple Instructor fields:

  1. Course title: CHEM 101 - Introduction to Chemistry
    Instructor: Mr. Smith
  2. Course title: CHEM 101 - Introduction to Chemistry
    Instructor: Ms. Jones

when Aggregating on the Instructor field, and Filtering on the Course Title field, the resulting view could look like:

  1. Course title: CHEM 101 - Introduction to Chemistry
    Instructor(s): Mr. Smith, Ms. Jones

Or, if there were multiple Course nodes (say, for multiple terms) the View may by default be:

  1. Course title: CHEM 101 - Introduction to Chemistry
    Instructor: Mr. Smith
    Term: Fall 2013
  2. Course title: CHEM 101 - Introduction to Chemistry
    Instructor: Ms. Jones
    Term: Winter 2013

when Filtering on the Course Title field, the view could look like:

  1. Course title: CHEM 101 - Introduction to Chemistry

(note, you may want to remove the Term field, since it no longer applies once we're purposely removing multiple term rows from the results)

Or, Aggregated on both Instructor and Term fields:

  1. Course title: CHEM 101 - Introduction to Chemistry
    Instructor(s): Mr. Smith, Ms. Jones
    Term(s): Fall 2013, Winter 2013

INSTALLATION

Activate the module, then administer a desired View. Under any field you want to affect, Edit the field and select the appropriate Aggregate or Filter option under the "Views Distinct Settings" section of the configuration form.

If you don't have have a good field to disambiguate "duplicate" rows, you can add a Global: Text and rewrite it with some combination of existing fields, like the rewrite values for a course title display: "[class_subject] [class_number] [class_title]". Be sure to enable the post-rendering option, or rewrites will not work!

KNOWN ISSUES/SHORTCOMINGS

These are on the To-Do list, but don't seem critical enough to prevent this module from helping a lot of people. Still, they may cause odd behavior, so it's best if folks know about them:

  1. Pager counts and the number of rows displayed are incorrect when filtering (removing) duplicates, and aggregation cannot aggregate fields from outside the scope of each page, since each page only has access to the rows on that page. This is a known issue without a fix for now. Results won't be scrambled, but fewer-than-expected results may show up on pagers; please test the outcome and choose if the pager is worth the oddness.
  2. Aggregating fields pre-render actually aggregates the base field in the query results, so any other display fields that in some way use those results will be using the aggregated versions. As far as I know there isn't another way to do this, because hook_views_post_execute() does not have access to the display fields, only the query result rows.
  3. Potential incompatibility with some style plugins: The "Use the rendered output of this field" option in Views Distinct may cause odd things to happen with some style plugins that change output when called twice (e.g. Views Slideshow - see #1956878: Interference with Views Slideshow). This is because Views Distinct needs to re-render the rows when it makes changes to the View output after the fields have been rendered. If you encounter this issue, uncheck the "Use the rendered output of this field" option.

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