feature: Group by and having statement in FHIR Path about onfhir HOT 1 CLOSED

We have implemented a FHIR path function with the following signature;

groupBy(groupingExpr: expression, aggregationExpr: expression)

The 'groupingExpr' is an expression that returns a key value for each item in the collection. Then items in the input collection are grouped based on the equality of these keys.

The 'aggregationExpr' is an expression that returns an aggregation value from the grouped items. The result is a JSON array that contains a JSON object for each group with the following elements;

• "bucket": Where the value is the key value extracted by groupingExpr for corresponding group
• "agg": Where the value is the aggregated value calculated by the aggregationExpr for the corresponding group

We have also implemented the following aggregation functions for ease of use;

sum(valueExtractorExpr: expression)
Extract the numeric value (Fhir Path Number) by appliying the valueExtractorExpr on each item in the input collection and sum the results.
e.g. Return the sum of observation values within a bundle for each patient
Bundle.entry.resource.filter($this is Observation).groupBy($this.subject.reference, sum(valueQuantity.value))

avg(valueExtractorExpr: expression)
Extract the numeric value by appliying the valueExtractorExpr on each item in the input collection and take the average of results.

min(valueExtractorExpr: expression)
Extract the numeric value by appliying the valueExtractorExpr on each item in the input collection and take the minimum.

max(valueExtractorExpr: expression)
Extract the numeric value by appliying the valueExtractorExpr on each item in the input collection and take the maximum.

from onfhir.