You could be forgiven for assuming filters and facets for search are the same thing. Both exist to serve the same purpose: narrowing down search results by eliminating results or pages that don’t match selected criteria.

While researching this post, we found that most definitions for filters and facets online were wildly disparate and in some cases, completely incorrect. Most seemed to lump them together as the same thing (granted, they are quite similar) but there are noteworthy differences between the two, particularly when it comes to discussing onsite search.

For clarity’s sake, we’re going to define them as follows: filters exclude results based on initial criteria and do not change with each search, while facets exclude using the properties from returned results and do change with each search.

Filters and facets explained

Filters

Filters are broad categories that are selected by the user to immediately eliminate pages or results on a site. They can be chosen before a search query has been entered, or immediately when presented with search results.

Unlike facets, filters never change between searches. They will always be the same and don't adjust to reflect the search results, so it’s important that these are configured to be as general as possible.

Filters can be displayed as tabs on a results page (think Google’s filters for Images, Shopping, Videos, and News), but even navigational elements in web pages are technically filters; when clicking on each of these what is displayed will match what has been selected, and the rest is "filtered out".

Because if you can’t explain it in emojis then it’s not worth explaining - a visual look at classifying foods using facets.

Facets

Facets are a bit more specific - they are filters but pertain exclusively to the results from a search. As they relate specifically to your query, you'll never find facets that are irrelevant or inconsistent with what is displayed. You'll see that different facets are displayed depending on what your query is, and what the returned results are.

Because multiple facets can be selected at once they are more efficient than selecting filters - this becomes apparent when searching through a high volume of pages.

In 2018 Google Images recently implemented facets that are automatically generated by artificial intelligence (AI). For example, a Google Image search for "samsung" will return the facets "gold", "galaxy s6 edge", "price", and "logo" - all relevant to the search query, and all predicted by AI.

Pretty cool right? We've had great success using AI-generated facets here at Sajari too - but more on this later.

If you see a number in parentheses beside any filterable attribute in a results page, then this is a good indication that it is a facet. This number matches how many search results each characteristic relates to. Bear in mind though that not all facets will follow this rule; this is just a visual clue.

Examples of filters and facets online:

Both filters and facets help users refine their search query, which allows ecommerce and information-rich sites to deliver a better onsite search experience.

The New York Times are using both filters and facets on its search results page. It’s easy to see how many “Type” facets correspond to the search query, and the option to exclude results by a date range uses the published time to filter articles.

Best Buy has used a facet to only show results in their “Cell Phone Cases" category, based on the query “iphone case”. The displayed facets are showing phone case compatibility and case type for iPhones only, taken from the query. If the user was to enter a different query, like "televisions" for example, the returned facets would match that query, and might instead be for resolution or screen size.

Best Buy also allows the user to filter the returned results based on each product's customer rating. As the user can exclude results based on each's star rating for every query, then this is a filter.

Amazon allows the user to select a filter as they enter their query in the search bar, before they execute the query. This means that the user doesn’t have to filter out products on the results page. Similar to the Best Buy example above, the user can filter out products based on price and customer review rating - these don’t change between searches.

Amazon uses facets quite interestingly. Searching for “electronics” shows facets for the different departments under Electronics (including "Television & Video" and "Electronics Cables") but also allows the user to show other departments, just in case the auto-selected facet is too specific. You can also use facets to shop by brand and model.

These examples show how filters and facets are used in different places online, but here are the main differences broken down:

Okay, I can see the difference now. Should I use filters and facets for my search?

As we can see, the area where filters and facets are the most useful is ecommerce search  - where keywords used to reign supreme, facets and filters are fast becoming more practical for search.

Of course, this isn't 100% true  -  using specific keywords when searching for things like brands is useful  -  but if you think about the last time you bought something online, it's highly likely you clicked on a filter and then narrowed down the results using facets to only show certain sizes or prices.

It's much easier to find an object or item using filters and facets;  it's nearly impossible to describe an item in a few keywords to such a degree where only one item is returned (we're still working on it though).

Research from Nielsen and Norman has confirmed the necessity of faceted search  -  when users are presented with too many choices, the product that they were looking for is missed and they will go elsewhere. Facets have become an integral part of shopping online and users will now complain when facets aren't available.

These days, ecommerce sites without faceted search are the exception, rather than the rule.

The standard facets for ecommerce are well known  -  price, size, color etc. - but facets are also useful whenever there is a large collection of content that has classifiable traits. If you were browsing through a collection of legal documents, it would be useful to facet by ruling date or jurisdiction. Similarly, if searching through an online music library facets like genre or song duration would be more useful.

Don't worry about returning too many facets either. Hick's Law states that users can easily scan a long list of facets as long as they are in order (usually alphabetical) and are all familiar.

Great, they sound useful. How can I start using filters and facets?

Setting up filters and facets may sound daunting, but as long as each page has a similar structure, filters and facets are quite easy to get up and running. Filters are often created using a site’s URL structure; this can be a straightforward way to allow users to quickly narrow down results, but it’s not a reliable method for creating rich facets to allow users to sort through large amounts of data.

At Sajari we're focused on giving you the tools to build your own onsite search experiences, customized to your own business. We’ve made setting up your own customized filters and facets as easy as possible. You can simply wrap any HTML element in Sajari tags to tell our crawler to store the element’s variables - these variables can then be used to create filters and facets in your search interfaces.

Sajari can also use artificial intelligence to classify information and generate facets automatically if you have a large swathe of unstructured data. AI can sort content into mathematical clusters that can be labeled, and any new content added to your site will be tagged with these labels. We won't go into the details here, but check out our blog on machine learning to get an overview of how we're using AI to create delightful search experiences.

Hopefully this blog has given you a better grasp of the difference between filters and facets, but to recap:

• Filters eliminate search results using initial criteria and never change between searches.
• Facets are used to refine search results using result attributes, and will change depending on the search query.

Filters and facets are expectations a user has when searching your site, store, or app. If you're not using filters and facets, you’re more likely to create a frustrating search experience which could lose you sales and customers. If you need any more clarification about filters and facets or how we can work with you to create a seamless search experience, feel free to reach out to us @Sajari.

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