Rth_element

aggregation-functions rth_element

syntax

  • rth_element(a,r)
  • rth_element(a, r, relation)

definition

  • rth_element(a, r) results in a parameter with the r * (n-1)th element of the ascending sorted data-item a (n = number of elements).
  • rth_element(a, r, relation) results in an attribute with the r * (n-1)th elements of the ascending sorted data item a, grouped by relation (n = number of elements within a partition). The domain-unit of the result is the values-unit of the relation. The values unit of the result should match the values unit of attribute a.

description

  • If r*(n-1) is not an integer, a weighted mean is calculated from the values that relate to the two nearest indices.
  • With r = 0.5, the function results in the median of data item a.

applies to

  • attribute a with Numeric, uint2, uint4 or bool value-type
  • data item r with float32 value type
  • relation with value type of the group CanBeDomainUnit

conditions

  1. The values unit of the resulting data item should match with regard to value type and metric with the values unit of attribute a.
  2. The domain of arguments a and relation must match
  3. The domain of argument r must be the same as the result domain or r must be a parameter.

since version

5.61

example 

1. parameter<uint32>  rth_elementNrInh := rth_element(City/NrInhabitants, 0.5f); result = 400
2. attribute<float32> rth_elementNrInhRegion (Region) := 
    rth_element(
       City/NrInhabitants
      ,0.5f
      ,City/Region_rel
   );
City/NrInhabitants City/Region_rel
550 0
525 1
300 2
500 1
200 3
175 null
null 3

domain City, nr of rows = 7

rth_elementNrInhRegion
550
512
300
200
null

domain Region, nr of rows = 5

see also