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There is a newer version: 3.2.1

#
# Custom Aggregate: standard deviation, median
# Olivier Corby - Wimmics Inria I3S - 2015
#
select 
  (aggregate(?v, us:sigma)  as ?sig)
  (aggregate(?v, us:median) as ?med)
  (aggregate(?v, us:avg)    as ?avg)
where {
  bind (unnest(xt:iota(999)) as ?v)
}

function us:median(?list){
  let (?l = xt:sort(?list)){
    xt:get(?l, xsd:integer((xt:size(?l) - 1) / 2))
  }
}

function us:sigma(?list){
  let (?avg = us:avg(?list),
       ?sum = apply (kg:plus, maplist(us:sqdiff, ?list, ?avg))){
    power(?sum / xt:size(?list), 0.5)
  }
}

function us:avg(?list){
  apply (kg:plus, ?list) / xt:size(?list) 
}

function us:sqdiff(?x, ?avg){
  power(?x - ?avg, 2)
}