Filter icon for "include null"

Question

I'm designing an e-commerce site that allows for filtering on items based on attributes such as weight, size, price, etc. The problem is for certain attributes, like "weight", some items have data, and others do not.

A user filtering by "weight" may want to be strict (only include items whose weight is known and in the desired range), or they may want to be lenient (include items whose weight is in the desired range, or unknown).

I could provide a checkbox that says "Include items with unknown weight", but would much rather have this be a tooltip on some sort of icon button. The problem is, I'm unsure of what icon to use.

I've looked through Google's Material Icons and cannot find anything that fits, nor can I even conceptualize what a good icon would look like. I'm hesitant to even mention the word "null" anywhere.

I'm stuck with three options:

1. Make an button that says "n/a", which is either pressed down, or not. The tooltip will will say "Including items with unknown weight"

   • Pros: Provides the user with the option.
   • Cons: Not simple. Another thing for the user to think about.

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2. Avoid this choice altogether and have no option. But what would the expected behavior be if the user is filtering by weight -- hide items with unknown weights, or show items with unknown weights?

   • Pros: Simple.
   • Cons: May not meet user's expectations. If hiding null values, may hide items the user cares about. If showing null values, may show too many null-weight items and give the appearance the filter is not working.

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3. Avoid the choice and have no options -- if they are filtering by weight, then show items with unknown weights, but also include some sort of warning symbol on the item indicating the weight is unknown.

   • Pros: Simple.
   • Cons: Results may contain too many items with no weights and cause the user to scan too much.

Answer 1

I think showing all items (including items with no weight value) as a first step is a good idea.

Give the user a call to action to exclude items with no weight value so that you make sure the user sees what he/she wants.

The call to action may be placed in places like:

• just under the weight filter.
• instead of the weight value in items cards.
• a full width button just above the items display grid (if it has a higher priority for users).

Answer 2

Filters are there to increase search result relevance. They have no other purpose in existing.

For this reason, most sites with filters will exclude unknown values when filtering by a field.

This is what users expect: if you filter by price from $100 to $200, you would not expect to see a page of results of donuts and new cars! You'd expect to see things which are explicitly priced between $100 and $200.

If you think a "n/a" button is valuable, then make it a separate story ticket to A/B test the idea once the basic design has been rolled out.