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<p>Hi,</p>

<p>I have a basic example using aggregates:</p>

<p>----------------------</p>

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

<p>-----------------------</p>

<p>But I still have two questions:</p>

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

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

<p>Thanks,</p>

<p>Andreas</p>

<p>On 2017-05-05 14:31, Neumann, Andreas wrote:</p>

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<p>Hi,</p>

<p>Does someone have an example how to use QgsVectorLayer.aggregate() from Python?</p>

<p>How would the syntax for the parameters in the QgsAggregateCalculator.calculate() method look like in Python?</p>

<p>Thanks,</p>

<p>Andreas</p>

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