---
type: "fhirpath-function"
title: "FHIRPath Function: isDistinct"
function: "isDistinct"
category: "Existence"
section: "5.1.12"
source: "fhirpath/functions.json"
---
# FHIRPath Function: isDistinct
Returns `true` if all the items in the input collection are distinct. To determine whether two items are distinct, the [equals](#equals) (`=`) operator is used, as defined below.

Conceptually, this function is shorthand for a comparison of the `count()` of the input collection against the `count()` of the `distinct()` of the input collection:

``` fhirpath
X.count() = X.distinct().count()
```

This means that if the input collection is empty (`{ }`), the result is `true`.
## Summary
- **Category**: Existence
- **Section**: `5.1.12`
- **Return Type**: `Boolean`
- **Empty Input Result**: `true`
- **Errors on Multiple Input**: `false`
## Description
Returns `true` if all the items in the input collection are distinct. To determine whether two items are distinct, the equals (`=`) operator is used.
## Arguments
- none
## Type Mapping
- `Any-Boolean`
## Example
```fhirpath
Patient.identifier.isDistinct() // returns true if all identifiers are unique
```