---
type: "fhirpath-function"
title: "FHIRPath Function: where"
function: "where"
category: "Filtering and projection"
section: "5.2.1"
source: "fhirpath/functions.json"
---
# FHIRPath Function: where
> This is a [scoped function](#scoped-functions): The `criteria` argument is evaluated for each item (setting `$this` and `$index` before each iteration); those that return `true` are included in the output collection.

Returns a collection containing only those items in the input collection for which the stated `criteria` expression evaluates to `true`. Items for which the expression evaluates to `false` or empty (`{ }`) are not included in the result.

If the input collection is empty (`{ }`), the result is empty.

If the result of evaluating the condition is other than a single boolean value, the evaluation will end and signal an error to the calling environment, consistent with singleton evaluation of collections behavior.

The following example returns the list of `telecom` elements that have a `use` element with the value of `'official'`:

``` fhirpath
Patient.telecom.where(use = 'official')
```

<a name="fn-select"></a>
## Summary
- **Category**: Filtering and projection
- **Section**: `5.2.1`
- **Return Type**: `collection`
- **Empty Input Result**: `empty`
- **Errors on Multiple Input**: `false`
## Description
Returns a collection containing only those elements in the input collection for which the stated `criteria` expression evaluates to `true`. Elements for which the expression evaluates to `false` or empty (`{ }`) are not included in the result.
## Arguments
- `criteria`: `expression` - Expression to filter the elements
## Type Mapping
- `Any-Any`
## Example
```fhirpath
Patient.telecom.where(use = 'official')
```