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

title	description	categories	menu	keywords	signature	relatedfuncs	aliases
complement	Returns the elements of the last collection that are not in any of the others.	functions	docs parent functions	collections	complement COLLECTION [COLLECTION]... collections.Complement COLLECTION [COLLECTION]...	intersect symdiff union

To find the elements within $c3 that do not exist in $c1 or $c2:

{{ $c1 := slice 3 }}
{{ $c2 := slice 4 5  }}
{{ $c3 := slice 1 2 3 4 5 }}

{{ complement $c1 $c2 $c3 }} → [1 2]

{{% note %}} Make your code simpler to understand by using a chained pipeline:

{{% /note %}}

{{ $c3 | complement $c1 $c2 }} → [1 2]

You can also use the complement function with page collections. Let's say your site has five content types:

content/
├── blog/
├── books/
├── faqs/
├── films/
└── songs/

To list everything except blog articles (blog) and frequently asked questions (faqs):

{{ $blog := where site.RegularPages "Type" "blog" }}
{{ $faqs := where site.RegularPages "Type" "faqs" }}
{{ range site.RegularPages | complement $blog $faqs }}
  <a href="{{ .RelPermalink }}">{{ .LinkTitle }}</a>
{{ end }}

{{% note %}} Although the example above demonstrates the complement function, you could use the where function as well:

{{% /note %}}

{{ range where site.RegularPages "Type" "not in" (slice "blog" "faqs") }}
  <a href="{{ .RelPermalink }}">{{ .LinkTitle }}</a>
{{ end }}

In this example we use the complement function to remove stop words from a sentence:

{{ $text := "The quick brown fox jumps over the lazy dog" }}
{{ $stopWords := slice "a" "an" "in" "over" "the" "under" }}
{{ $filtered := split $text " " | complement $stopWords }}

{{ delimit $filtered " " }} → The quick brown fox jumps lazy dog