---
type: "fhirpath-function"
title: "FHIRPath Function: subsetOf"
function: "subsetOf"
category: "Existence"
section: "5.1.8"
source: "fhirpath/functions.json"
---
# FHIRPath Function: subsetOf
Returns `true` if all items in the input collection are members of the collection passed as the `other` argument. Membership is determined using the [equals](#equals) (`=`) operation.

Conceptually, this function is evaluated by testing each item in the input collection for membership in the `other` collection, with a default of `true`. This means that if the input collection is empty (`{ }`), the result is `true`, otherwise if the `other` collection is empty (`{ }`), the result is `false`.

The following example returns `true` if the tags defined in any contained resource are a subset of the tags defined in the MedicationRequest resource:

``` fhirpath
MedicationRequest.contained.meta.tag.subsetOf(MedicationRequest.meta.tag)
```
## Summary
- **Category**: Existence
- **Section**: `5.1.8`
- **Return Type**: `Boolean`
- **Empty Input Result**: `true`
- **Errors on Multiple Input**: `false`
## Description
Returns `true` if all items in the input collection are members of the collection passed as the `other` argument. Membership is determined using the equals (`=`) operation.
## Arguments
- `other`: `collection` - Collection to check membership against
## Type Mapping
- `Any-Boolean`
## Example
```fhirpath
MedicationRequest.contained.meta.tag.subsetOf(MedicationRequest.meta.tag)
```