Union_data

Relational functions union_data

syntax

definition

union_data(domain unit, a, b, .. n) results in a new Attribute with as Domain unit the first Argument: domainunit.

The resulting attribute contains the values of the data items a, b, .., n.

description

The first argument domainunit, is often made with the Union_unit function.

The union_data function results in an attribute with as Values unit the values units of data items a, b, ..n and as Domain unit the first argument of the function (domainunit). In other words, it appends b to a and then c to a and b, etc.

union_data(newdomain, att_old_domain) can be used to convert attributes from a source to a target domain unit.

applies to

  • Unit domainunit with Value type from the group CanBeDomainUnit
  • data items a, b, … n with Numeric, Point, uint2, uint4, bool or string value type

conditions

  • The values unit of data items a, b, … n must match.

performance

O(n₁ + n₂ + … + nₖ) where nᵢ = number of elements in data item i. Single pass copying data from each source.

example 

unit<uint32> HollandCity := union_unit(NHCity, ZHCity)
{
   attribute<string> name := union_data(., NHCity/name, ZHCity/name);
}
HollandCity/name
Amsterdam
Haarlem
Alkmaar
Rotterdam
DenHaag
Leiden
Dordrecht
Leiden

domain HollandCity, nr of rows = 8

NHCity/name
Amsterdam
Haarlem
Alkmaar

domain NHCity, nr of rows = 3

ZHCity/name
Rotterdam
DenHaag
Leiden
Dordrecht
Leiden

domain ZHCity, nr of rows = 5

see also