gohugoio-hugo/docs/content/en/functions/complement.md

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title	description	date	categories	menu	keywords	signature	hugoversion	aliases
complement	`collections.Complement` (alias `complement`) gives the elements of a collection that are not in any of the others.	2018-11-07	functions	docs parent functions	collections intersect union	COLLECTION | complement COLLECTION [COLLECTION]...	0.51

Example:

{{ $pages := .Site.RegularPages | first 50 }}
{{ $news := where $pages "Type" "news" | first 5 }}
{{ $blog := where $pages "Type" "blog" | first 5 }}
{{ $other := $pages | complement $news $blog | first 10 }}

The above is an imaginary use case for the home page where you want to display different page listings in sections/boxes on different places on the page: 5 from news, 5 from the blog and then 10 of the pages not shown in the other listings, to complement them.