Median

ordering-functions median

definition

The median of an attribute in the GeoDMS can be calculated with the rth_element function, with as second argument the value 0.5.

The median function in the GeoDMS calculates the middle value for each row of three given attributes. Thus median(a, b, c) :=

median(a, interval([min_elem](min_elem.html)(b, c), [max_elem](max_elem.html)(b, c))) :=
a < min_elem(b, c)
    ? min_elem(b, c)
    : max_elem(b, c) < a
       ? max_elem(b, c)
       : a

This can be used to bind a to a given range of allowed values.

syntax

  • median(a, b, c)

conditions

  1. the domain-unit arguments a, b, and c must match or be void.
  2. the values-unit of arguments a, b, and c must match.
  3. b is known to be not larger than c.

since version

since 2008

example

attribute<uint32> medianABC (ADomain) := median(A, B, C);
A(int32) B(int32) C(int32) medianABC
0 1 2 1
1 -1 4 1
-2 2 2 2
4 0 7 4
999 111 -5 111
null 0 0 0
0 null 0 0
0 0 null 0
null 0 null 0
null null null null

ADomain, nr of rows = 10

In earlier versions (before 7.202) a null value in one of the arguments could result in a null value of the resulting data item. This now only occurs if all arguments have null values. This is a results of the implementation of min_elem and max_elem as functions that since then return the minimum defined value of each row.