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hugo/docs/content/en/functions/collections/Where.md

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---
title: collections.Where
description: Returns the given collection, removing elements that do not satisfy the comparison condition.
categories: []
keywords: []
action:
aliases: [where]
related: []
returnType: any
signatures: ['collections.Where COLLECTION KEY [OPERATOR] VALUE']
toc: true
aliases: [/functions/where]
---
The `where` function returns the given collection, removing elements that do not satisfy the comparison condition. The comparison condition is composed of the `KEY`, `OPERATOR`, and `VALUE` arguments:
```text
collections.Where COLLECTION KEY [OPERATOR] VALUE
--------------------
comparison condition
```
Hugo will test for equality if you do not provide an `OPERATOR` argument. For example:
```go-html-template
{{ $pages := where .Site.RegularPages "Section" "books" }}
{{ $books := where .Site.Data.books "genres" "suspense" }}
```
## Arguments
The where function takes three or four arguments. The `OPERATOR` argument is optional.
COLLECTION
: (`any`) A [page collection] or a [slice] of [maps].
[maps]: /getting-started/glossary/#map
[page collection]: /getting-started/glossary/#page-collection
[slice]: /getting-started/glossary/#slice
KEY
: (`string`) The key of the page or map value to compare with `VALUE`. With page collections, commonly used comparison keys are `Section`, `Type`, and `Params`. To compare with a member of the page `Params` map, [chain] the subkey as shown below:
```go-html-template
{{ $result := where .Site.RegularPages "Params.foo" "bar" }}
```
[chain]: /getting-started/glossary/#chain
OPERATOR
: (`string`) The logical comparison [operator](#operators).
VALUE
: (`any`) The value with which to compare. The values to compare must have comparable data types. For example:
Comparison|Result
:--|:--
`"123" "eq" "123"`|`true`
`"123" "eq" 123`|`false`
`false "eq" "false"`|`false`
`false "eq" false`|`true`
When one or both of the values to compare is a slice, use the `in`, `not in`, or `intersect` operators as described below.
## Operators
Use any of the following logical operators:
`=`, `==`, `eq`
: (`bool`) Reports whether the given field value is equal to `VALUE`.
`!=`, `<>`, `ne`
: (`bool`) Reports whether the given field value is not equal to `VALUE`.
`>=`, `ge`
: (`bool`) Reports whether the given field value is greater than or equal to `VALUE`.
`>`, `gt`
: `true` Reports whether the given field value is greater than `VALUE`.
`<=`, `le`
: (`bool`) Reports whether the given field value is less than or equal to `VALUE`.
`<`, `lt`
: (`bool`) Reports whether the given field value is less than `VALUE`.
`in`
: (`bool`) Reports whether the given field value is a member of `VALUE`. Compare string to slice, or string to string. See&nbsp;[details](/functions/collections/in).
`not in`
: (`bool`) Reports whether the given field value is not a member of `VALUE`. Compare string to slice, or string to string. See&nbsp;[details](/functions/collections/in).
`intersect`
: (`bool`) Reports whether the given field value (a slice) contains one or more elements in common with `VALUE`. See&nbsp;[details](/functions/collections/intersect).
`like` {{< new-in 0.116.0 >}}
: (`bool`) Reports whether the given field value matches the regular expression specified in `VALUE`. Use the `like` operator to compare `string` values. The `like` operator returns `false` when comparing other data types to the regular expression.
{{% note %}}
The examples below perform comparisons within a page collection, but the same comparisons are applicable to a slice of maps.
{{% /note %}}
## String comparison
Compare the value of the given field to a [`string`]:
[`string`]: /getting-started/glossary/#string
```go-html-template
{{ $pages := where .Site.RegularPages "Section" "eq" "books" }}
{{ $pages := where .Site.RegularPages "Section" "ne" "books" }}
```
## Numeric comparison
Compare the value of the given field to an [`int`] or [`float`]:
[`int`]: /getting-started/glossary/#int
[`float`]: /getting-started/glossary/#float
```go-html-template
{{ $books := where site.RegularPages "Section" "eq" "books" }}
{{ $pages := where $books "Params.price" "eq" 42 }}
{{ $pages := where $books "Params.price" "ne" 42.67 }}
{{ $pages := where $books "Params.price" "ge" 42 }}
{{ $pages := where $books "Params.price" "gt" 42.67 }}
{{ $pages := where $books "Params.price" "le" 42 }}
{{ $pages := where $books "Params.price" "lt" 42.67 }}
```
## Boolean comparison
Compare the value of the given field to a [`bool`]:
[`bool`]: /getting-started/glossary/#bool
```go-html-template
{{ $books := where site.RegularPages "Section" "eq" "books" }}
{{ $pages := where $books "Params.fiction" "eq" true }}
{{ $pages := where $books "Params.fiction" "eq" false }}
{{ $pages := where $books "Params.fiction" "ne" true }}
{{ $pages := where $books "Params.fiction" "ne" false }}
```
## Member comparison
Compare a [`scalar`] to a [`slice`].
[`scalar`]: /getting-started/glossary/#scalar
[`slice`]: /getting-started/glossary/#slice
For example, to return a collection of pages where the `color` page parameter is either "red" or "yellow":
```go-html-template
{{ $fruit := where site.RegularPages "Section" "eq" "fruit" }}
{{ $colors := slice "red" "yellow" }}
{{ $pages := where $fruit "Params.color" "in" $colors }}
```
To return a collection of pages where the "color" page parameter is neither "red" nor "yellow":
```go-html-template
{{ $fruit := where site.RegularPages "Section" "eq" "fruit" }}
{{ $colors := slice "red" "yellow" }}
{{ $pages := where $fruit "Params.color" "not in" $colors }}
```
## Intersection comparison
Compare a [`slice`] to a [`slice`], returning collection elements with common values. This is frequently used when comparing taxonomy terms.
For example, to return a collection of pages where any of the terms in the "genres" taxonomy are "suspense" or "romance":
```go-html-template
{{ $books := where site.RegularPages "Section" "eq" "books" }}
{{ $genres := slice "suspense" "romance" }}
{{ $pages := where $books "Params.genres" "intersect" $genres }}
```
## Regular expression comparison
{{< new-in 0.116.0 >}}
To return a collection of pages where the "author" page parameter begins with either "victor" or "Victor":
```go-html-template
{{ $pages := where .Site.RegularPages "Params.author" "like" `(?i)^victor` }}
```
{{% include "functions/_common/regular-expressions.md" %}}
{{% note %}}
Use the `like` operator to compare string values. Comparing other data types will result in an empty collection.
{{% /note %}}
## Date comparison
### Predefined dates
There are four predefined front matter dates: [`date`], [`publishDate`], [`lastmod`], and [`expiryDate`]. Regardless of the front matter data format (TOML, YAML, or JSON) these are [`time.Time`] values, allowing precise comparisons.
[`date`]: /methods/page/date/
[`publishdate`]: /methods/page/publishdate/
[`lastmod`]: /methods/page/lastmod/
[`expirydate`]: /methods/page/expirydate/
[`time.Time`]: https://pkg.go.dev/time#Time
For example, to return a collection of pages that were created before the current year:
```go-html-template
{{ $startOfYear := time.AsTime (printf "%d-01-01" now.Year) }}
{{ $pages := where .Site.RegularPages "Date" "lt" $startOfYear }}
```
### Custom dates
With custom front matter dates, the comparison depends on the front matter data format (TOML, YAML, or JSON).
{{% note %}}
Using TOML for pages with custom front matter dates enables precise date comparisons.
{{% /note %}}
With TOML, date values are first-class citizens. TOML has a date data type while JSON and YAML do not. If you quote a TOML date, it is a string. If you do not quote a TOML date value, it is [`time.Time`] value, enabling precise comparisons.
In the TOML example below, note that the event date is not quoted.
{{< code file="content/events/2024-user-conference.md" >}}
+++
title = '2024 User Conference"
eventDate = 2024-04-01
+++
{{< /code >}}
To return a collection of future events:
```go-html-template
{{ $events := where .Site.RegularPages "Type" "events" }}
{{ $futureEvents := where $events "Params.eventDate" "gt" now }}
```
When working with YAML or JSON, or quoted TOML values, custom dates are strings; you cannot compare them with `time.Time` values. String comparisons may be possible if the custom date layout is consistent from one page to the next. To be safe, filter the pages by ranging through the collection:
```go-html-template
{{ $events := where .Site.RegularPages "Type" "events" }}
{{ $futureEvents := slice }}
{{ range $events }}
{{ if gt (time.AsTime .Params.eventDate) now }}
{{ $futureEvents = $futureEvents | append . }}
{{ end }}
{{ end }}
```
## Nil comparison
To return a collection of pages where the "color" parameter is present in front matter, compare to `nil`:
```go-html-template
{{ $pages := where .Site.RegularPages "Params.color" "ne" nil }}
```
To return a collection of pages where the "color" parameter is not present in front matter, compare to `nil`:
```go-html-template
{{ $pages := where .Site.RegularPages "Params.color" "eq" nil }}
```
In both examples above, note that `nil` is not quoted.
## Nested comparison
These are equivalent:
```go-html-template
{{ $pages := where .Site.RegularPages "Type" "tutorials" }}
{{ $pages = where $pages "Params.level" "eq" "beginner" }}
```
```go-html-template
{{ $pages := where (where .Site.RegularPages "Type" "tutorials") "Params.level" "eq" "beginner" }}
```
## Portable section comparison
Useful for theme authors, avoid hardcoding section names by using the `where` function with the [`MainSections`] method on a `Site` object.
[`MainSections`]: /methods/site/mainsections/
```go-html-template
{{ $pages := where .Site.RegularPages "Section" "in" .Site.MainSections }}
```
With this construct, a theme author can instruct users to specify their main sections in the site configuration:
{{< code-toggle file=hugo >}}
[params]
mainSections = ['blog','galleries']
{{< /code-toggle >}}
If `params.mainSections` is not defined in the site configuration, the `MainSections` method returns a slice with one element---the top level section with the most pages.
## Boolean/undefined comparison
Consider this site content:
```text
content/
├── posts/
│ ├── _index.md
│ ├── post-1.md <-- front matter: exclude = false
│ ├── post-2.md <-- front matter: exclude = true
│ └── post-3.md <-- front matter: exclude not defined
└── _index.md
```
The first two pages have an "exclude" field in front matter, but the last page does not. When testing for _equality_, the third page is _excluded_ from the result. When testing for _inequality_, the third page is _included_ in the result.
### Equality test
This template:
```go-html-template
<ul>
{{ range where .Site.RegularPages "Params.exclude" "eq" false }}
<li><a href="{{ .RelPermalink }}">{{ .LinkTitle }}</a></li>
{{ end }}
</ul>
```
Is rendered to:
```html
<ul>
<li><a href="/posts/post-1/">Post 1</a></li>
</ul>
```
This template:
```go-html-template
<ul>
{{ range where .Site.RegularPages "Params.exclude" "eq" true }}
<li><a href="{{ .RelPermalink }}">{{ .LinkTitle }}</a></li>
{{ end }}
</ul>
```
Is rendered to:
```html
<ul>
<li><a href="/posts/post-2/">Post 2</a></li>
</ul>
```
### Inequality test
This template:
```go-html-template
<ul>
{{ range where .Site.RegularPages "Params.exclude" "ne" false }}
<li><a href="{{ .RelPermalink }}">{{ .LinkTitle }}</a></li>
{{ end }}
</ul>
```
Is rendered to:
```html
<ul>
<li><a href="/posts/post-2/">Post 2</a></li>
<li><a href="/posts/post-3/">Post 3</a></li>
</ul>
```
This template:
```go-html-template
<ul>
{{ range where .Site.RegularPages "Params.exclude" "ne" true }}
<li><a href="{{ .RelPermalink }}">{{ .LinkTitle }}</a></li>
{{ end }}
</ul>
```
Is rendered to:
```html
<ul>
<li><a href="/posts/post-1/">Post 1</a></li>
<li><a href="/posts/post-3/">Post 3</a></li>
</ul>
```
To exclude a page with an undefined field from a boolean _inequality_ test:
1. Create a collection using a boolean comparison
2. Create a collection using a nil comparison
3. Subtract the second collection from the first collection using the [`collections.Complement`] function.
[`collections.Complement`]: /functions/collections/complement/
This template:
```go-html-template
{{ $p1 := where .Site.RegularPages "Params.exclude" "ne" true }}
{{ $p2 := where .Site.RegularPages "Params.exclude" "eq" nil }}
<ul>
{{ range $p1 | complement $p2 }}
<li><a href="{{ .RelPermalink }}">{{ .LinkTitle }}</a></li>
{{ end }}
</ul>
```
Is rendered to:
```html
<ul>
<li><a href="/posts/post-1/">Post 1</a></li>
</ul>
```
This template:
```go-html-template
{{ $p1 := where .Site.RegularPages "Params.exclude" "ne" false }}
{{ $p2 := where .Site.RegularPages "Params.exclude" "eq" nil }}
<ul>
{{ range $p1 | complement $p2 }}
<li><a href="{{ .RelPermalink }}">{{ .LinkTitle }}</a></li>
{{ end }}
</ul>
```
Is rendered to:
```html
<ul>
<li><a href="/posts/post-1/">Post 2</a></li>
</ul>
```
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