---
type: "fhirpath-function"
title: "FHIRPath Function: aggregate"
function: "aggregate"
category: "Aggregates"
section: "7.1"
source: "fhirpath/functions.json"
---
# FHIRPath Function: aggregate
_No canonical section match found in index.md._
## Summary
- **Category**: Aggregates
- **Section**: `7.1`
- **Return Type**: `value`
- **Empty Input Result**: `empty`
- **Errors on Multiple Input**: `false`
## Description
Performs general-purpose aggregation by evaluating the aggregator expression for each element of the input collection. Within this expression, the standard iteration variables of `$this` and `$index` can be accessed, but also a `$total` aggregation variable.
## Arguments
- `aggregator`: `expression` - Expression to evaluate for each element
- `init` (optional): `value` - Initial value for the accumulator
## Type Mapping
- n/a
## Example
```fhirpath
value.aggregate($this + $total, 0)
```