Combine_data

Relational functions combine_data

syntax

  • combine_data (combined_domain, a_rel, b_rel)

definition

combine_data(combined_domain, a_rel, b_rel) results in an Attribute with Index numbers to the combined_domain Argument, combining the values of data items a_rel and b_rel.

description

The first argument combined_domain is usually made with a Combine function.

The combine_data function results in an attribute with an index to combined_domain for each element of the domain of a_rel and b_rel, with as Values unit the first Argument of the function (combined_domain) and as Domain unit the domain unit of the data items a_rel and b_rel.

applies to

  • Unit combined_domain with value type from the group CanBeDomainUnit.
  • attributes a_rel, b_rel with value type from group CanBeDomainUnit.

conditions

  • The domain units of the data items a_rel and b_rel must match (or be all Void).
  • values unit of b_rel must match the 2nd argument of the combine or combine_unit with which the combined_domain has been defined.

since version

7.131

performance

O(n) where n = number of elements in the domain of a_rel and b_rel. Single pass computing combined index from input relations.

combining multiple indices

combine_data can only be used to combine two indices.

When 3 (or more) indices need to be combined, chain them:

unit<uint32>   BC               := combine_unit(B,  C);
unit<uint32>   ABC              := combine_unit(A, BC);
attribute<ABC> ABC_rel (domain) := combine_data(ABC, domain/A_rel, combine_data(BC, domain/B_rel, domain/C_rel));

example 

unit<uint32> NHCityYear := combine(NHCity, YearDomain);
attribute<NHCityYear> NHCityYear_rel (Adomain) := combine_data(NHCityYear, NHCity_rel, YearDomain_rel);
NHCity_rel YearDomain_rel NHCity Year NHCityYear_rel
0 0 Amsterdam 1995 0
0 1 Amsterdam 2005 3
1 1 Haarlem 2005 4
2 0 Alkmaar 1995 2
2 1 Alkmaar 2005 5

ADomain, nr of rows = 5

nr_1 nr_2 NHCityName Year
0 0 Amsterdam 1995
0 1 Amsterdam 2005
1 0 Haarlem 1995
1 1 Haarlem 2005
2 0 Alkmaar 1995
2 1 Alkmaar 2005

domain NHCityYear, nr of rows = 6

NHCity/name
Amsterdam
Haarlem
Alkmaar

domain NHCity, nr of rows = 3

YearDomain/Year
1995
2005

Yeardomain, nr of rows = 2

see also