this may be solved already. Indeed, I've seen it solved on other sites. Here's an example.
If I have a collection for "Red Wines", then within that, if I select "France" from the filter in that collection, I still get regions or grapes which don't apply to France.
Now, Shopify doesn't have a hierarchy of tags, as far as I can see.
So, in picking France, I should only see filters for French regions (others shouldn't display).
How do I best go about this? Is it moving to collections rather than tags for filtering on product lists?
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This is Jay here from Oakleaf Infoway. We would love to help you with the filters of the product and make it run seamlessly within the hierarchy
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In your example, it's using this app to build the filter: https://apps.shopify.com/product-filter-search
So if you are not familiar with code, you should use that app.
If you're familiar with code or trying to do this your self:
On your screenshot I see you already have the filter showing. If you make that without using any app and only customize the default filter-by-tag function of Shopify, after filtering by a tag, it will point to a sub page/URL of current collection.
Eg: on collection-wine when clicking on tag-france it will redirect to collection-wine/tag-france
So on that sub page, you can check the variable collection.all_tags. It will contains all tag that belongs to products on that sub collection.
After that you can check each tag on the Grape list compare with collection.all_tags then hide the tag if collection.all_tags doesn't contain it.
You can refer to Shopify tutorial for filter by product tag https://shopify.dev/tutorials/customize-theme-filter-collections-with-product-tags. However, it’s not possible to apply more than one filter within the same group. You can try some third party filter app such as Collection Filter & Search Bar, Filters & Instant Search to set up dynamic product filtering that shows the relevant filters based on the viewing products.