collect_by_cond

relational-functions collect_by_cond

syntax

  1. collect_by_cond(selection unit: S, condition: D -> Bool, values-attribute: D -> V)
  2. collect_by_cond(selection unit: S, values-attribute: D -> V)

definition

ad 1: collect_by_cond(selection unit: S, condition: D -> Bool, values-attribute: D -> V) results in an attribute S-> V with those values in values-attribute than correspond with the true-values of condition. Note that the cardinality of S must correspond with the number of true values in condition. This is always the case when S is defined as select(condition), or select_with_org_rel(condition).

ad 2: collect_by_cond(selection unit: S, values-attribute: D -> V) is defined as 1 when S has a calculation rule that resolves to select(condition), or select_with_org_rel(condition). If S has been defined otherwise, an error message will indicate that no operator could be found.

applies to

  • selection domain unit: a unit with value-type of the group CanbeDomainUnit
  • condition: must be a boolean attribute or subexpression resulting in boolean values.
  • attribute: can be any attribute with the same domain unit as the condition argument

since version

8.8.0

example 

unit<uint32> City: StorageName = "city.csv", StorageType = "gdal.vect", StorageReadOnly = "True"
{
   attribute<string> name;
   attribute<uint32> RegionCode;
}
unit<uint32> ZHCities := select_with_attr_by_cond(City, City/RegionCode == 200);

attribute<string> name (ZHCities) := collect_by_cond(ZHCities, City/RegionCode == 200, City/name);
City/RegionCode City/Name
100 Amsterdam
200 Rotterdam
300 Utrecht
200 Den Haag
400 Eindhoven
null Haarlem
400 Tilburg

domain City, nr of rows = 7

name
Rotterdam
Den Haag

domain ZHCities, nr of rows = 2

see also