mdnif.sql

drop  function if exists _final_mdnif(int[]) cascade;
CREATE OR REPLACE FUNCTION _final_mdnif(int[])
   RETURNS numeric AS
$$
DECLARE
  sum numeric;
  i int;
  j int;
  N int;
  K int;
BEGIN
  sum := 0;
  K = array_length($1,1);
  -- undefined for zero arrays
  IF K = 0 OR K IS NULL THEN
     RETURN NULL;
  END IF;
  -- equal to 0 if one only
  IF K = 1 THEN
     RETURN 0;
  END IF;
  -- compute N
  N = 0;
  FOR i IN 1..K LOOP
     N := N + $1[i];
  END LOOP;
  -- otherwise compute according to Wilcox paper

  FOR i IN 1..K-1 LOOP
     FOR j IN i+1..K LOOP
        sum := sum + @($1[i] - $1[j]);
     END LOOP;
  END LOOP;
  RETURN 1.0 - (1.0/(N * (K-1))) * sum;
END
$$
LANGUAGE 'plpgsql' IMMUTABLE;
 
CREATE AGGREGATE mdnif(int) (
  SFUNC=array_append,
  STYPE=int[],
  FINALFUNC=_final_mdnif,
  INITCOND='{}'
);