First
aggregation-functions first
syntax
- first(a)
- first(a, relation)
definition
- first(a) results in a parameter with the first of the non null values of attribute a.
- first(a, relation) results in an attribute with the first of the non null values of attribute a, grouped by relation. The domain-unit of the resulting attribute is the values-unit of the relation.
applies to
- attribute a with Numeric, Point, string or bool value-type
- relation with value type of the group CanBeDomainUnit
conditions
- The values unit of the resulting data item should match with regard to value type and metric with the values unit of attribute a.
- The domain of argument a and relation must match.
example
parameter<uint32> firstNrInh := first(City/NrInhabitants); result = 550
parameter<string> firstCityName := first(City/CityName); result = ‘Amsterdam’
parameter<bool> firstIsCap := first(City/IsCapital); result = True
attribute<uint32> firstNrInhRegion (Region) := first(City/NrInhabitants, City/Region_rel);
attribute<string> firstCityNameRegion (Region) := first(City/CityName, City/Region_rel);
attribute<bool> firstIsCapital (Region) := first(City/IsCapital, City/Region_rel);
| City/NrInhabitants | City/CityName | IsCapital | City/Region_rel |
|---|---|---|---|
| 550 | Amsterdam | True | 0 |
| 525 | Rotterdam | False | 1 |
| 300 | Utrecht | False | 2 |
| 500 | DenHaag | False | 1 |
| 200 | Eindhoven | False | 3 |
| 175 | Haarlem | False | null |
| null | null | False | 3 |
domain City, nr of rows = 7
| firstNrInhRegion | firstCityNameRegion | firstIsCapitalRegion |
|---|---|---|
| 550 | Amsterdam | True |
| 525 | Rotterdam | False |
| 300 | Utrecht | False |
| 200 | Eindhoven | False |
| null | null | False |
domain Region, nr of rows = 5