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Clarify the append function
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jmooring authored Aug 25, 2023
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88 changes: 75 additions & 13 deletions content/en/functions/append.md
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---
title: append
description: "`append` appends one or more values to a slice and returns the resulting slice."
description: Appends one or more elements to a slice and returns the resulting slice.
categories: [functions]
menu:
docs:
parent: functions
keywords: [collections]
signature: ["COLLECTION | append VALUE [VALUE]...", "COLLECTION | append COLLECTION"]
signature: ["COLLECTION | append ELEMENT [ELEMENT]...", "COLLECTION | append COLLECTION"]
relatedfuncs: [last,first,where,slice]
---

An example appending single values:
This function appends all elements, excluding the last, to the last element. This allows [pipe](/getting-started/glossary/#pipeline) constructs as shown below.

Append a single element to a slice:

```go-html-template
{{ $s := slice "a" "b" }}
{{ $s }} → [a b]
{{ $s = $s | append "c" }}
{{ $s }} → [a b c]
```

Append two elements to a slice:

```go-html-template
{{ $s := slice "a" "b" }}
{{ $s }} → [a b]
{{ $s = $s | append "c" "d" }}
{{ $s }} → [a b c d]
```

Append two elements, as a slice, to a slice. This produces the same result as the previous example:

```go-html-template
{{ $s := slice "a" "b" "c" }}
{{ $s = $s | append "d" "e" }}
{{/* $s now contains a []string with elements "a", "b", "c", "d", and "e" */}}
{{ $s := slice "a" "b" }}
{{ $s }} → [a b]
{{ $s = $s | append (slice "c" "d") }}
{{ $s }} → [a b c d]
```

The same example appending a slice to a slice:
Start with an empty slice:

```go-html-template
{{ $s := slice "a" "b" "c" }}
{{ $s := slice }}
{{ $s }} → []
{{ $s = $s | append "a" }}
{{ $s }} → [a]
{{ $s = $s | append "b" "c" }}
{{ $s }} → [a b c]
{{ $s = $s | append (slice "d" "e") }}
{{ $s }} → [a b c d e]
```

If a slice contains other slices, further slices will be appended as values:
If you start with a slice of a slice:

```go-html-template
{{ $s := slice (slice "a" "b") (slice "c" "d") }}
{{ $s = $s | append (slice "e" "f") (slice "g" "h") }}
{{/* $s now contains a [][]string containing four slices: ["a" "b"], ["c" "d"], ["e" "f"], and ["g" "h"] */}}
{{ $s := slice (slice "a" "b") }}
{{ $s }} → [[a b]]
{{ $s = $s | append (slice "c" "d") }}
{{ $s }} → [[a b] [c d]]
```

To create a slice of slices, starting with an empty slice:

```go-html-template
{{ $s := slice }}
{{ $s }} → []
{{ $s = $s | append (slice (slice "a" "b")) }}
{{ $s }} → [[a b]]
{{ $s = $s | append (slice "c" "d") }}
{{ $s }} → [[a b] [c d]]
```

The `append` function works for all types, including `Pages`.


Although the elements in the examples above are strings, you can use the `append` function with any data type, include Pages. For example, on the home page of a corporate site, to display links to the two most recent press releases followed by links to the four most recent articles:

```go-html-template
{{ $p := where site.RegularPages "Type" "press-releases" | first 2 }}
{{ $p = $p | append (where site.RegularPages "Type" "articles" | first 4) }}
{{ with $p }}
<ul>
{{ range $p }}
<li><a href="{{ .RelPermalink }}">{{ .LinkTitle }}</a></li>
{{ end }}
</ul>
{{ end }}
```

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