Code for section which generates related products based on grouping tags - https://www.shopify.com/partners/blog/related-products

related-products-by-tag-group.liquid

{% if section.settings.show_related_products == true %}
<hr>
<div class="product-template__container page-width" itemscope itemtype="http://schema.org/Product" id="ProductSection-{{ section.id }}" data-section-id="{{ section.id }}" data-section-type="product" data-enable-history-state="true">
 
{% comment %}
  Number of related items per row,
  and number of rows.
{% endcomment %}

{% assign number_of_related_products_per_row = section.settings.related_grid_num %}
{% assign number_of_rows = section.settings.related_grid_row %}

{% comment %}
  Heading.
  Leave blank if you don't need one.
{% endcomment %}

{% assign heading = section.settings.related_title %}

{% comment %}
  Set either or both to true, if you want
  to limit yourself to items with same vendor, and/or type.
{% endcomment %}

{% assign same_vendor = false %}
{% assign same_type = false %}

{% comment %}
  Collections to ignore.
  Never pick related items from those.
{% endcomment %}

{% assign exclusions = 'frontpage,all' | split: ',' %}

{% comment %}
  Looking for a relevant collection.
{% endcomment %}

{% if product.metafields.c_f['Related Products'] %}
  {% assign collection = collections[product.metafields.c_f['Related Products']] %}
{% endif %}

{% assign found_a_collection = false %}
{% if collection and collection.all_products_count > 1 %}
  {% unless exclusions contains collection.handle %}
    {% assign found_a_collection = true %}
  {% endunless %}
{% endif %}
{% unless found_a_collection %}
  {% for c in product.collections %}
    {% unless exclusions contains c.handle or c.all_products_count < 2 %}
      {% assign found_a_collection = true %}
      {% assign collection = c %}
      {% break %}
    {% endunless %}
  {% endfor %}
{% endunless %}

{% comment %}
  If we have a relevant collection.
{% endcomment %}

{% if found_a_collection %}

  {% assign counter = 0 %}
  {% assign break_at = number_of_rows | times: number_of_related_products_per_row %}
  {% assign current_product = product %}
  
  {% case number_of_related_products_per_row %}
    {% when '1' %}
      {% assign grid_item_width = '' %}
        {%- assign max_height = 700 -%}
    {% when '2' %}
      {% assign grid_item_width = 'small--one-half medium-up--one-half' %}
      {%- assign max_height = 530 -%}
    {% when '3' %}
      {% assign grid_item_width = 'small--one-half medium-up--one-third' %}
      {%- assign max_height = 345 -%}
    {% when '4' %}
      {% assign grid_item_width = 'small--one-half medium-up--one-quarter' %}
      {%- assign max_height = 250 -%}
    {% when '5' %}
      {% assign grid_item_width = 'small--one-half medium-up--one-fifth' %}
      {%- assign max_height = 195 -%}
    {% when '6' %}
      {% assign grid_item_width = 'small--one-half medium-up--one-sixth' %}
      {%- assign max_height = 195 -%}
    {% else %}
      {% assign grid_item_width = 'small--one-half medium-up--one-quarter' %}
      {%- assign max_height = 195 -%}
  {% endcase %}


  {% capture related_items %}
<div class="grid grid--uniform{% if collection.products_count > 0 %} grid--view-items{% endif %}">
  
  {% for product in collections.all.products %}
  {% unless product.handle == current_product.handle %}
  {% unless same_vendor and current_product.vendor != product.vendor %}
  {% unless same_type and current_product.type != product.type %}
  {% comment %} 
    Replace 'test' below with prefered tag 
  {% endcomment %}
  {% if product.tags contains  'test' %} 
  <div class="grid__item {{ grid_item_width }}">
    {% include 'product-card-grid', max_height: max_height %}
  </div>
  {% assign counter = counter | plus: 1 %}
  {% if counter == break_at %}
  {% break %}
  {% endif %}
  {% endif %}
  {% endunless %}
  {% endunless %}
  {% endunless %}
  {% endfor %}
  
</div>
  {% endcapture %}

  {% assign related_items = related_items | trim %}

  {% unless related_items == blank %}

  <aside class="grid">
    <div class="grid__item">
      {% unless heading == blank %}
      <header class="section-header">
        <h3>{{ heading }}</h3>
      </header>
      {% endunless %}
      <div class="grid-uniform">
        {{ related_items }}
      </div>
    </div>
  </aside>

  {% endunless %}
     
{% endif %}
  
</div>
{% endif %}

{% schema %}
{
  "name": "Related products",
  "settings": [
    {
      "type": "checkbox",
      "id": "show_related_products",
      "label": "Show related products",
      "default": false
    },
    {
      "id": "related_title",
      "type": "text",
      "label": "Section title",
      "default": "Other fine products"
    },
    {
      "type": "select",
      "id": "related_grid_num",
      "label": "Products per row (Desktop)",
      "default": "4",
      "options": [
        {
          "value": "2",
          "label": "2"
        },
        {
          "value": "3",
          "label": "3"
        },
        {
          "value": "4",
          "label": "4"
        },
        {
          "value": "5",
          "label": "5"
        }
      ]
    },
    {
      "type": "select",
      "id": "related_grid_row",
      "label": "Number of rows (Desktop)",
      "default": "1",
      "options": [
        {
          "value": "1",
          "label": "1"
        },
        {
          "value": "2",
          "label": "2"
        },
        {
          "value": "3",
          "label": "3"
        }
      ]
    }
  ]
}
{% endschema %}