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[processing] add Extract by expression algorithm as combination
of "Select by expression" and "Save selected features" does not work in modeler
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‎python/plugins/processing/algs/qgis/ExtractByExpression.py

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# -*- coding: utf-8 -*-
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"""
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***************************************************************************
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ExtractByExpression.py
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---------------------
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Date : September 2017
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Copyright : (C) 2017 by Alexander Bruy
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Email : alexander dot bruy at gmail dot com
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***************************************************************************
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* *
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* This program is free software; you can redistribute it and/or modify *
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* it under the terms of the GNU General Public License as published by *
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* the Free Software Foundation; either version 2 of the License, or *
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* (at your option) any later version. *
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* *
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***************************************************************************
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"""
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__author__ = 'Alexander Bruy'
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__date__ = 'September 2017'
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__copyright__ = '(C) 2017, Alexander Bruy'
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# This will get replaced with a git SHA1 when you do a git archive
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__revision__ = '$Format:%H$'
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from qgis.core import QgsExpression, QgsExpressionContext, QgsExpressionContextUtils, QgsFeatureRequest
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from processing.core.GeoAlgorithm import GeoAlgorithm
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from processing.core.GeoAlgorithmExecutionException import GeoAlgorithmExecutionException
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from processing.core.parameters import ParameterVector
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from processing.core.parameters import ParameterString
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from processing.core.outputs import OutputVector
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from processing.tools import dataobjects
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class ExtractByExpression(GeoAlgorithm):
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INPUT = 'INPUT'
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EXPRESSION = 'EXPRESSION'
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OUTPUT = 'OUTPUT'
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def defineCharacteristics(self):
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self.name, self.i18n_name = self.trAlgorithm('Extract by expression')
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self.group, self.i18n_group = self.trAlgorithm('Vector selection tools')
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self.addParameter(ParameterVector(self.INPUT,
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self.tr('Input Layer'), [ParameterVector.VECTOR_TYPE_ANY]))
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self.addParameter(ParameterString(self.EXPRESSION,
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self.tr("Expression")))
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self.addOutput(OutputVector(self.OUTPUT, self.tr('Extracted (expression)')))
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def processAlgorithm(self, progress):
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layer = layer = dataobjects.getObjectFromUri(self.getParameterValue(self.INPUT))
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expression = self.getParameterValue(self.EXPRESSION)
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qExp = QgsExpression(expression)
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if qExp.hasParserError():
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raise GeoAlgorithmExecutionException(qExp.parserErrorString())
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writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(
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layer.fields(), layer.wkbType(), layer.crs())
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context = QgsExpressionContext()
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context.appendScope(QgsExpressionContextUtils.globalScope())
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context.appendScope(QgsExpressionContextUtils.projectScope())
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context.appendScope(QgsExpressionContextUtils.layerScope(layer))
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count = layer.featureCount()
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step = 100.0 / count if count else 1
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request = QgsFeatureRequest(qExp, context)
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for current, f in enumerate(layer.getFeatures(request)):
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writer.addFeature(f)
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progress.setPercentage(int(current * step))
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del writer

‎python/plugins/processing/algs/qgis/QGISAlgorithmProvider.py

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@@ -55,6 +55,7 @@
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from .RandomExtract import RandomExtract
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from .RandomExtractWithinSubsets import RandomExtractWithinSubsets
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from .ExtractByLocation import ExtractByLocation
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from .ExtractByExpression import ExtractByExpression
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from .PointsInPolygon import PointsInPolygon
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from .PointsInPolygonUnique import PointsInPolygonUnique
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from .PointsInPolygonWeighted import PointsInPolygonWeighted
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ZonalStatistics(), PointsFromPolygons(),
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PointsFromLines(), RandomPointsExtent(),
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RandomPointsLayer(), RandomPointsPolygonsFixed(),
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RandomPointsPolygonsVariable(),
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RandomPointsPolygonsVariable(), ExtractByExpression(),
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RandomPointsAlongLines(), PointsToPaths(),
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PostGISExecuteSQL(), ImportIntoPostGIS(),
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SetVectorStyle(), SetRasterStyle(),

‎python/plugins/processing/tests/testdata/expected/extract_expression.gml

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<?xml version="1.0" encoding="utf-8" ?>
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<ogr:FeatureCollection
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://ogr.maptools.org/ extract_expression.xsd"
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xmlns:ogr="http://ogr.maptools.org/"
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xmlns:gml="http://www.opengis.net/gml">
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<gml:boundedBy>
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<gml:Box>
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<gml:coord><gml:X>4</gml:X><gml:Y>-3</gml:Y></gml:coord>
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<gml:coord><gml:X>10</gml:X><gml:Y>5</gml:Y></gml:coord>
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</gml:Box>
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</gml:boundedBy>
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<gml:featureMember>
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<ogr:extract_expression fid="polys.1">
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<ogr:geometryProperty><gml:Polygon srsName="EPSG:4326"><gml:outerBoundaryIs><gml:LinearRing><gml:coordinates>5,5 6,4 4,4 5,5</gml:coordinates></gml:LinearRing></gml:outerBoundaryIs></gml:Polygon></ogr:geometryProperty>
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<ogr:name>Aaaaa</ogr:name>
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<ogr:intval>-33</ogr:intval>
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<ogr:floatval>0.00000</ogr:floatval>
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</ogr:extract_expression>
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</gml:featureMember>
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<gml:featureMember>
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<ogr:extract_expression fid="polys.3">
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<ogr:geometryProperty><gml:Polygon srsName="EPSG:4326"><gml:outerBoundaryIs><gml:LinearRing><gml:coordinates>6,1 10,1 10,-3 6,-3 6,1</gml:coordinates></gml:LinearRing></gml:outerBoundaryIs><gml:innerBoundaryIs><gml:LinearRing><gml:coordinates>7,0 7,-2 9,-2 9,0 7,0</gml:coordinates></gml:LinearRing></gml:innerBoundaryIs></gml:Polygon></ogr:geometryProperty>
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<ogr:name>ASDF</ogr:name>
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<ogr:intval>0</ogr:intval>
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<ogr:floatval xsi:nil="true"/>
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</ogr:extract_expression>
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</gml:featureMember>
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</ogr:FeatureCollection>

‎python/plugins/processing/tests/testdata/expected/extract_expression.xsd

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<?xml version="1.0" encoding="UTF-8"?>
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<xs:schema targetNamespace="http://ogr.maptools.org/" xmlns:ogr="http://ogr.maptools.org/" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:gml="http://www.opengis.net/gml" elementFormDefault="qualified" version="1.0">
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<xs:import namespace="http://www.opengis.net/gml" schemaLocation="http://schemas.opengis.net/gml/2.1.2/feature.xsd"/>
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<xs:element name="FeatureCollection" type="ogr:FeatureCollectionType" substitutionGroup="gml:_FeatureCollection"/>
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<xs:complexType name="FeatureCollectionType">
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<xs:complexContent>
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<xs:extension base="gml:AbstractFeatureCollectionType">
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<xs:attribute name="lockId" type="xs:string" use="optional"/>
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<xs:attribute name="scope" type="xs:string" use="optional"/>
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</xs:extension>
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</xs:complexContent>
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</xs:complexType>
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<xs:element name="extract_expression" type="ogr:extract_expression_Type" substitutionGroup="gml:_Feature"/>
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<xs:complexType name="extract_expression_Type">
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<xs:complexContent>
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<xs:extension base="gml:AbstractFeatureType">
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<xs:sequence>
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<xs:element name="geometryProperty" type="gml:PolygonPropertyType" nillable="true" minOccurs="0" maxOccurs="1"/>
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<xs:element name="name" nillable="true" minOccurs="0" maxOccurs="1">
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<xs:simpleType>
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<xs:restriction base="xs:string">
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<xs:maxLength value="255"/>
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</xs:restriction>
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</xs:simpleType>
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</xs:element>
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<xs:element name="intval" nillable="true" minOccurs="0" maxOccurs="1">
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<xs:simpleType>
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<xs:restriction base="xs:integer">
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<xs:totalDigits value="10"/>
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</xs:restriction>
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</xs:simpleType>
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</xs:element>
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<xs:element name="floatval" nillable="true" minOccurs="0" maxOccurs="1">
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<xs:simpleType>
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<xs:restriction base="xs:decimal">
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<xs:totalDigits value="21"/>
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<xs:fractionDigits value="5"/>
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</xs:restriction>
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</xs:simpleType>
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</xs:element>
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</xs:sequence>
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</xs:extension>
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</xs:complexContent>
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</xs:complexType>
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</xs:schema>

‎python/plugins/processing/tests/testdata/qgis_algorithm_tests.yaml

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OUTPUT:
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name: expected/single_to_multi.gml
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type: vector
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- algorithm: qgis:extractbyexpression
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name: Test (qgis:extractbyexpression)
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params:
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EXPRESSION: left("Name", 1) = 'A'
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INPUT:
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name: polys.gml
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type: vector
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results:
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OUTPUT:
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name: expected/extract_expression.gml
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type: vector

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