Often, in facetted filtering experiences, on mobile, the filters are tucked offscreen. To indicate that the current view is being filtered, often the filter button is presented with a number indicating how many active filters are applied. ex: [ Filters (2) ]
This number is inconsistent from retailer to retailer. It can be either:
- the number of selected filter values
- the number of filter categories with filter values selected in them.
Amazon represents the number of filter categories selected:
- Brand: Intel & AMD
- Shipping: Free
- Cores: 2, 4 & 8
Walmart represents the number of filter values selected:
- Brand: Apple & Sony
- Shipping: Free
- Colour: Grey, Pink, White
As far as I'm concerned - the biggest usability gain comes from having anything indicating an active filter state - the exact count isn't that essential.
Pro Filter Category
- Numbers past a certain point don't really matter
- It may be more important to know the number of categories, rather than values
- When you open the filter button, you tend to see categories - tap 3, see 3 selected things
Pro Filter Value
- Every time the filter changes, the number is guaranteed to change
- It's a simple sum and may match user mental models.
From my audit around the web, it's about 50/50 and I guess either one works, but is there any other arguments that can work in favour of one or the other approach?