Hugo collections.Where

The where function returns the given slice, removing elements that do not satisfy the comparison condition. The comparison condition is composed of the KEY, OPERATOR, and VALUE arguments:

collections.Where SLICE 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.

SLICE

([]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:

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 slice 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 slice 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 elements with common values. This is frequently used when comparing taxonomy terms.

For example, to return a slice 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 slice of pages where the “author” page parameter begins with either “victor” or “Victor”:

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

在指定正则表达式时，使用原始 [字符串字面量]（反引号）而不是解释字符串字面量（双引号）以简化语法。使用解释字符串字面量时，您必须转义反斜杠。

Go 的正则表达式包实现了 [RE2 语法]。RE2 语法是 PCRE 接受的内容的子集（粗略地说），并带有各种 [注意事项]。请注意，不支持 RE2 \C 转义序列。

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 slice 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.

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

To return a slice 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 over the slice:

{{ $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 slice 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 slice 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:

mainSections:
- blog
- galleries

mainSections = ['blog', 'galleries']

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

If 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:

1. Create a slice using a boolean comparison
2. Create a slice using a nil comparison
3. Subtract the second slice from the first slice 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>