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+---
+title: collections.Union
+linkTitle: union
+description: Given two arrays or slices, returns a new array that contains the elements or objects that belong to either or both arrays/slices.
+categories: [functions]
+keywords: []
+menu:
+  docs:
+    parent: functions
+function:
+  aliases: [union]
+  returnType: any
+  signatures: [collections.Union SET1 SET2]
+relatedFunctions:
+  - collections.Complement
+  - collections.Intersect
+  - collections.SymDiff
+  - collections.Union
+aliases: [/functions/union] 
+---
+
+Given two arrays (or slices) A and B, this function will return a new array that contains the elements or objects that belong to either A or to B or to both. The elements supported are strings, integers, and floats (only float64).
+
+```go-html-template
+{{ union (slice 1 2 3) (slice 3 4 5) }}
+<!-- returns [1 2 3 4 5] -->
+
+{{ union (slice 1 2 3) nil }}
+<!-- returns [1 2 3] -->
+
+{{ union nil (slice 1 2 3) }}
+<!-- returns [1 2 3] -->
+
+{{ union nil nil }}
+<!-- returns an error because both arrays/slices have to be of the same type -->
+```
+
+## OR filter in where query
+
+This is also very useful to use as `OR` filters when combined with where:
+
+```go-html-template
+{{ $pages := where .Site.RegularPages "Type" "not in" (slice "page" "about") }}
+{{ $pages = $pages | union (where .Site.RegularPages "Params.pinned" true) }}
+{{ $pages = $pages | intersect (where .Site.RegularPages "Params.images" "!=" nil) }}
+```
+
+The above fetches regular pages not of `page` or `about` type unless they are pinned. And finally, we exclude all pages with no `images` set in Page parameters.
+
+See [intersect](/functions/collections/intersect) for `AND`.