---
type: "fhirpath-function"
title: "FHIRPath Function: comparable"
function: "comparable"
category: "Comparison"
section: "6.2.5"
source: "fhirpath/functions.json"
---
# FHIRPath Function: comparable
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> **Note:** The contents of this section are Standard for Trial Use (STU)
{: .stu-note }

Returns `true` if the input Quantity can be compared with the `other` Quantity and their relationship to each other determined.
Comparable means that both have values, and the units are the same (irrespective of the system), or both have `code` and `system` values,
and the `system` is recognized by the FHIRPath implementation, and the codes are comparable within that system
(e.g. `'d'` (days) and `'h'` (hours), or `'[in_i]'` (inches) and `'cm'` (centimeters)).
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If either or both inputs are empty, or either input is not a single Quantity value, the result is empty (`{ }`).
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``` fhirpath
1 'mg'.comparable(2 'mg') // true - these types are comparable
1 'm'.comparable(20 'cm') // true - these types are both metric distance measures
2 '1'.comparable(3) // true - the integer will implicitly convert to a Quantity with unit `'1'` which is the same system/code so is comparable
1.comparable(2) // true - these will both convert to quantities with the same system/code, hence are comparable
```
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This function can be used to guard comparison operations to prevent returning empty results when the quantities are not comparable:
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``` fhirpath
iif(Observation.value.comparable(2 'mg'), Observation.value < 2 'mg', {})
```
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## Summary
- **Category**: Comparison
- **Section**: `6.2.5`
- **Return Type**: `Boolean`
- **Empty Input Result**: `empty`
- **Errors on Multiple Input**: `true`
## Description
Returns `true` if the input Quantity can be compared with the `other` Quantity and their relationship to each other determined. Comparable means that both have values, and the units are the same (irrespective of the system), or both have `code` and `system` values, and the `system` is recognized by the FHIRPath implementation, and the codes are comparable within that system.
## Arguments
- `other`: `Quantity` - The Quantity to check comparability against
## Type Mapping
- `Quantity-Boolean`
## Example
```fhirpath
1 'mg'.comparable(2 'mg') // true - these types are comparable
1 'm'.comparable(20 'cm') // true - these types are both metric distance measures
iif(Observation.value.comparable(2 'mg'), Observation.value < 2 'mg', {})
```