---
type: "fhirpath-operator"
title: "FHIRPath Operator: | (union)"
operator: "|"
category: "Collections"
section: "6.4.1"
source: "fhirpath/operations.json"
---
# FHIRPath Operator: | (union)
Merge the two collections into a single collection, eliminating any duplicate values (using [equals](#equals) (`=`)) to determine equality). There is no expectation of order in the resulting collection.

See the [union](#unionother-collection) function for more detail.
## Summary
- **Category**: Collections
- **Section**: `6.4.1`
- **Left Argument**: `collection`
- **Right Argument**: `collection`
- **Return Type**: `collection`
- **Empty Input Result**: `empty`
- **Errors on Multiple Input**: `false`
## Description
Merge the two collections into a single collection, eliminating any duplicate values (using equals `=` to determine equality). There is no expectation of order in the resulting collection.
## Type Mapping
- `collection-collection`