collections.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:

collections.Where COLLECTION KEY [OPERATOR] VALUE
                             --------------------
                             comparison condition

Hugo will test for equality if you do not provide an OPERATOR argument. For example:

{{ $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].
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:

{{ $result := where .Site.RegularPages "Params.foo" "bar" }}

OPERATOR: (string) The logical comparison operator.
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 details.
not in: (bool) Reports whether the given field value is not a member of VALUE. Compare string to slice, or string to string. See details.
intersect: (bool) Reports whether the given field value (a slice) contains one or more elements in common with VALUE. See details.
like: (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.

String comparison #

Compare the value of the given field to a [string]:

{{ $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]:

{{ $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]:

{{ $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].

For example, to return a collection of pages where the color page parameter is either “red” or “yellow”:

{{ $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”:

{{ $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”:

{{ $books := where site.RegularPages "Section" "eq" "books" }}

{{ $genres := slice "suspense" "romance" }}
{{ $pages := where $books "Params.genres" "intersect" $genres }}

Regular expression comparison #

To return a collection of pages where the “author” page parameter begins with either “victor” or “Victor”:

{{ $pages := where .Site.RegularPages "Params.author" "like" `(?i)^victor` }}

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.

For example, to return a collection of pages that were created before the current year:

{{ $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).

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.

content/events/2024-user-conference.md

+++
title = '2024 User Conference"
eventDate = 2024-04-01
+++

To return a collection of future events:

{{ $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:

{{ $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:

{{ $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:

{{ $pages := where .Site.RegularPages "Params.color" "eq" nil }}

In both examples above, note that nil is not quoted.

Nested comparison #

These are equivalent:

{{ $pages := where .Site.RegularPages "Type" "tutorials" }}
{{ $pages = where $pages "Params.level" "eq" "beginner" }}

{{ $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.

{{ $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:

hugo.

params:
  mainSections:
  - blog
  - galleries

[params]
  mainSections = ['blog', 'galleries']

{
   "params": {
      "mainSections": [
         "blog",
         "galleries"
      ]
   }
}

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:

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:

<ul>
  {{ range where .Site.RegularPages "Params.exclude" "eq" false }}
    <li><a href="{{ .RelPermalink }}">{{ .LinkTitle }}</a></li>
  {{ end }}
</ul>

Is rendered to:

<ul>
  <li><a href="/posts/post-1/">Post 1</a></li>
</ul>

This template:

<ul>
  {{ range where .Site.RegularPages "Params.exclude" "eq" true }}
    <li><a href="{{ .RelPermalink }}">{{ .LinkTitle }}</a></li>
  {{ end }}
</ul>

Is rendered to:

<ul>  
  <li><a href="/posts/post-2/">Post 2</a></li>
</ul>

Inequality test #

This template:

<ul>
  {{ range where .Site.RegularPages "Params.exclude" "ne" false }}
    <li><a href="{{ .RelPermalink }}">{{ .LinkTitle }}</a></li>
  {{ end }}
</ul>

Is rendered to:

<ul>
  <li><a href="/posts/post-2/">Post 2</a></li>
  <li><a href="/posts/post-3/">Post 3</a></li>
</ul>

This template:

<ul>
  {{ range where .Site.RegularPages "Params.exclude" "ne" true }}
    <li><a href="{{ .RelPermalink }}">{{ .LinkTitle }}</a></li>
  {{ end }}
</ul>

Is rendered to:

<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:

Create a collection using a boolean comparison
Create a collection using a nil comparison
Subtract the second collection from the first collection using the [collections.Complement] function.

This 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:

<ul>
  <li><a href="/posts/post-1/">Post 1</a></li>
</ul>

This 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:

<ul>
  <li><a href="/posts/post-1/">Post 2</a></li>
</ul>

collections.Where

Returns the given collection, removing elements that do not satisfy the comparison condition.

Arguments #

Operators #

String comparison #

Numeric comparison #

Boolean comparison #

Member comparison #

Intersection comparison #

Regular expression comparison #

Date comparison #

Predefined dates #

Custom dates #

Nil comparison #

Nested comparison #

Portable section comparison #

Boolean/undefined comparison #

Equality test #

Inequality test #