Working with multiple categories group, show not empty from only one category group

Question

I am having trouble showing a list of map categories that are not empty but they must work in conjunction with the countries category group

No children categories needed

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My categories setup

• Map group
  • Topographic
  • Geophysical
  • Geology

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• Countries group
  • Kenya
  • South Africa
  • Tanzania

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Eg:

• Entry one - Kenya & Geology
• Entry two - Kenya & Geology
• Entry three - Kenya & Geophysical

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My result should be on this address

url: /maps/category/kenya

• Geophysical
• Geology

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Any ideas, no luck with native categories and Gwcode categories tags. Any help is appreciated.

Answer 1

Leaving my solution here

I have used low2seg plugin and query. Little messy but it works.

{exp:query sql="select * from exp_categories as ec where ec.`cat_id` in (select distinct cat_id from `exp_category_posts` where entry_id in (select entry_id from `exp_category_posts` where cat_id = {segment_3_category_id})) and group_id = 1"} <option value="{cat_id}">{cat_name}</option> {/exp:query}

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At the end of the query, ensure you choose selected cat_id and group_id

where cat_id = {segment_3_category_id})) and group_id = 1"