Custom Page Template to show posts grouped by selected categories using ACF’s Taxonomy field in Genesis

Recently a user enquired:

Hi Sridhar,

I have a quick question for you (possible new project). I noticed that this site (drupal) https://www.switchbacktravel.com/outdoor-gear-reviews breaks its archive pages into section.
I wanted to know if something like that was possible in wordpress.

to which I replied:

Yes possible.

The easiest way would be to create a custom widget area, display it on a Page (using a Page Template) and drop several Genesis Featured Posts widgets with each widget showing posts from a specific category.

and he came back saying:

Thanks for getting back. I have a question from a management perspective. I will probably need 10+ of these type of pages so trying to manage the widgets areas from the Wordpress widget area could become cumbersome. Is there a way to have the widgets areas in the page editor? So when I edit the page using the custom templ to change the widgets. Hope that makes sense.

I wrote him:

In that case, the best way would be to use ACF to set up a custom category selector meta box in the Page editor and code the custom Page Template to output posts grouped by the selected categories.

This tutorial provides the steps to set up a Taxonomy custom field using Advanced Custom Fields Pro attached to Pages and when one or more categories is/are selected, a specific number of posts from the selected category/categories will be made to appear on the Page below the existing content using a custom Page Template in Genesis.

We shall use CSS Grid to arrange the posts in each group in a 3-column grid.

Step 1

Install and activate Advanced Custom Fields Pro.

Create a field group named say, "Page Meta" having a Category Selector taxonomy field.

Set the Taxonomy to category. Set Term Object as the return value.

Field group export file.

Step 2

Add the following in child theme's functions.php:

/**
 * Custom excerpt length.
 *
 * @link http://stackoverflow.com/a/17177847
 *
 * @param int $limit The number of words.
 */
function excerpt( $limit ) {
    return wp_trim_words( get_the_excerpt(), $limit );
}

Step 3

Create a file named say, template-category-groups.php in the child theme directory having the following: