hugo/content/en/functions/complement.md

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

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

```go-html-template
{{ $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]:

[chained pipeline]: https://pkg.go.dev/text/template#hdr-Pipelines
{{% /note %}}


```go-html-template
{{ $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:

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

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

```go-html-template
{{ $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:

[`where`]: /functions/where/
{{% /note %}} 

```go-html-template
{{ 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:

```go-html-template
{{ $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
```

[stop words]: https://en.wikipedia.org/wiki/Stop_word