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79 lines
2 KiB
Markdown
79 lines
2 KiB
Markdown
---
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title: complement
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description: Returns the elements of the last collection that are not in any of the others.
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categories: [functions]
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menu:
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docs:
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parent: functions
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keywords: [collections]
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signature:
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- "complement COLLECTION [COLLECTION]..."
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- "collections.Complement COLLECTION [COLLECTION]..."
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relatedfuncs: [intersect,symdiff,union]
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---
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To find the elements within `$c3` that do not exist in `$c1` or `$c2`:
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```go-html-template
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{{ $c1 := slice 3 }}
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{{ $c2 := slice 4 5 }}
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{{ $c3 := slice 1 2 3 4 5 }}
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{{ complement $c1 $c2 $c3 }} → [1 2]
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```
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{{% note %}}
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Make your code simpler to understand by using a [chained pipeline]:
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[chained pipeline]: https://pkg.go.dev/text/template#hdr-Pipelines
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{{% /note %}}
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```go-html-template
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{{ $c3 | complement $c1 $c2 }} → [1 2]
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```
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You can also use the `complement` function with page collections. Let's say your site has five content types:
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```text
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content/
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├── blog/
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├── books/
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├── faqs/
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├── films/
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└── songs/
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```
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To list everything except blog articles (`blog`) and frequently asked questions (`faqs`):
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```go-html-template
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{{ $blog := where site.RegularPages "Type" "blog" }}
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{{ $faqs := where site.RegularPages "Type" "faqs" }}
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{{ range site.RegularPages | complement $blog $faqs }}
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<a href="{{ .RelPermalink }}">{{ .LinkTitle }}</a>
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{{ end }}
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```
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{{% note %}}
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Although the example above demonstrates the `complement` function, you could use the [`where`] function as well:
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[`where`]: /functions/where/
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{{% /note %}}
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```go-html-template
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{{ range where site.RegularPages "Type" "not in" (slice "blog" "faqs") }}
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<a href="{{ .RelPermalink }}">{{ .LinkTitle }}</a>
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{{ end }}
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```
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In this example we use the `complement` function to remove [stop words] from a sentence:
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```go-html-template
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{{ $text := "The quick brown fox jumps over the lazy dog" }}
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{{ $stopWords := slice "a" "an" "in" "over" "the" "under" }}
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{{ $filtered := split $text " " | complement $stopWords }}
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{{ delimit $filtered " " }} → The quick brown fox jumps lazy dog
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```
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[stop words]: https://en.wikipedia.org/wiki/Stop_word
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