--- title: collections.Where description: Returns a slice by filtering the given slice based on a key, operator, and value. categories: [] keywords: [] params: functions_and_methods: aliases: [where] returnType: '[]any' signatures: ['collections.Where SLICE KEY [OPERATOR] VALUE'] aliases: [/functions/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: ```text collections.Where SLICE 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 hugo.Data.books "genres" "suspense" }} ``` ## Arguments The where function takes three or four arguments. The `OPERATOR` argument is optional. `SLICE` : (`[]any`) A [page collection](g) or a [slice](g) of [maps](g). `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](g) the subkey as shown below: ```go-html-template {{ $result := where .Site.RegularPages "Params.foo" "bar" }} ``` `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. `not in` : (`bool`) Reports whether the given field value is not a member of `VALUE`. Compare string to slice, or string to string. `intersect` : (`bool`) Reports whether the given field value (a slice) contains one or more elements in common with `VALUE`. `like` : (`bool`) Reports whether the given field value matches the [regular expression](g) 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. ## String comparison Compare the value of the given field to a [`string`](g): ```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`](g) or [`float`](g): ```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`](g): ```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`](g) to a [`slice`](g). For example, to return a slice 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 slice 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 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": ```go-html-template {{ $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": ```go-html-template {{ $pages := where .Site.RegularPages "Params.author" "like" `(?i)^victor` }} ``` {{% include "/_common/functions/regular-expressions.md" %}} > [!NOTE] > Use the `like` operator to compare string values. Comparing other data types will result in an empty slice. ## 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: ```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. 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. ```md {file="content/events/2024-user-conference.md"} +++ title = '2024 User Conference" eventDate = 2024-04-01 +++ ``` To return a slice 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 over the slice: ```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 slice 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 slice 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. ```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 their project configuration: {{< code-toggle file=hugo >}} mainSections = ['blog','galleries'] {{< /code-toggle >}} If `mainSections` is not defined in your project configuration, the `MainSections` method returns a slice with one element---the top-level section with the most pages. ## Boolean/undefined comparison Consider this project structure: ```tree 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 ``` Is rendered to: ```html ``` This template: ```go-html-template ``` Is rendered to: ```html ``` ### Inequality test This template: ```go-html-template ``` Is rendered to: ```html ``` This template: ```go-html-template ``` Is rendered to: ```html ``` To exclude a page with an undefined field from a boolean _inequality_ test: 1. Create a slice using a boolean comparison 1. Create a slice using a nil comparison 1. Subtract the second slice from the first slice using the [`collections.Complement`][] function. This template: ```go-html-template {{ $p1 := where .Site.RegularPages "Params.exclude" "ne" true }} {{ $p2 := where .Site.RegularPages "Params.exclude" "eq" nil }} ``` Is rendered to: ```html ``` This template: ```go-html-template {{ $p1 := where .Site.RegularPages "Params.exclude" "ne" false }} {{ $p2 := where .Site.RegularPages "Params.exclude" "eq" nil }} ``` Is rendered to: ```html ``` [`MainSections`]: /methods/site/mainsections/ [`collections.Complement`]: /functions/collections/complement/ [`date`]: /methods/page/date/ [`lastmod`]: /methods/page/lastmod/ [`time.Time`]: https://pkg.go.dev/time#Time