Type your Fhirpath expression below

try things like:
sum Patient.telecom.rank.aggregate($total+$this, 0)
avg Patient.select(telecom.rank.aggregate($total+$this, 0) / telecom.rank.count())
min Patient.telecom.rank.aggregate(iif($total.empty(), $this, iif($this < $total, $this, $total))) These are aggregates from the fhirpath spec