[QGIS-Developer] Python example with aggregate calculation

[Neumann, Andreas]

Hi, 

I have a basic example using aggregates: 

---------------------- 

@qgsfunction(args='auto', group='Custom', usesgeometry=False)
def get_ews_anlage_nr(gemeinde, feature, parent):
AnlageLayer =
QgsMapLayerRegistry.instance().mapLayersByName('Anlage')[0]
maxVal = AnlageLayer.aggregate(4,'to_int(substr("anlage_nr",4,4))')[0]
return maxVal 

----------------------- 

But I still have two questions: 

1. I still struggle to define a filter. I can't find the correct syntax
how to define that filter string. 

2. the first parameter "4" stands for "Max" aggregate (according to
http://qgis-python.kartoza.com/docs/core/other/QgsAggregateCalculator.html#class-qgsaggregatecalculator
). Could this code be written more "readable" by specifying "Max"
instead of 4? 

Thanks, 

Andreas 

On 2017-05-05 14:31, Neumann, Andreas wrote:

> Hi, 
> 
> Does someone have an example how to use QgsVectorLayer.aggregate() from Python? 
> 
> How would the syntax for the parameters in the QgsAggregateCalculator.calculate() method look like in Python? 
> 
> Thanks, 
> 
> Andreas
> 
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