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Merge pull request #5167 from alexbruy/extract-by-expression 
 [processing] add Extract by expression algorithm to QGIS 2.18
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@alexbruy
alexbruy committed Sep 12, 2017
2 parents 88dc615 + c8aceb2 commit 684e1da
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78 python/plugins/processing/algs/qgis/ExtractByExpression.py
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@@ -0,0 +1,78 @@
# -*- coding: utf-8 -*-

"""
***************************************************************************
ExtractByExpression.py
---------------------
Date : September 2017
Copyright : (C) 2017 by Alexander Bruy
Email : alexander dot bruy at gmail dot com
***************************************************************************
* *
* This program is free software; you can redistribute it and/or modify *
* it under the terms of the GNU General Public License as published by *
* the Free Software Foundation; either version 2 of the License, or *
* (at your option) any later version. *
* *
***************************************************************************
"""

__author__ = 'Alexander Bruy'
__date__ = 'September 2017'
__copyright__ = '(C) 2017, Alexander Bruy'

# This will get replaced with a git SHA1 when you do a git archive

__revision__ = '$Format:%H$'

from qgis.core import QgsExpression, QgsExpressionContext, QgsExpressionContextUtils, QgsFeatureRequest
from processing.core.GeoAlgorithm import GeoAlgorithm
from processing.core.GeoAlgorithmExecutionException import GeoAlgorithmExecutionException
from processing.core.parameters import ParameterVector
from processing.core.parameters import ParameterString
from processing.core.outputs import OutputVector
from processing.tools import dataobjects


class ExtractByExpression(GeoAlgorithm):

INPUT = 'INPUT'
EXPRESSION = 'EXPRESSION'
OUTPUT = 'OUTPUT'

def defineCharacteristics(self):
self.name, self.i18n_name = self.trAlgorithm('Extract by expression')
self.group, self.i18n_group = self.trAlgorithm('Vector selection tools')

self.addParameter(ParameterVector(self.INPUT,
self.tr('Input Layer'), [ParameterVector.VECTOR_TYPE_ANY]))
self.addParameter(ParameterString(self.EXPRESSION,
self.tr("Expression")))
self.addOutput(OutputVector(self.OUTPUT, self.tr('Extracted (expression)')))

def processAlgorithm(self, progress):
layer = layer = dataobjects.getObjectFromUri(self.getParameterValue(self.INPUT))

expression = self.getParameterValue(self.EXPRESSION)
qExp = QgsExpression(expression)
if qExp.hasParserError():
raise GeoAlgorithmExecutionException(qExp.parserErrorString())

writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(
layer.fields(), layer.wkbType(), layer.crs())

context = QgsExpressionContext()
context.appendScope(QgsExpressionContextUtils.globalScope())
context.appendScope(QgsExpressionContextUtils.projectScope())
context.appendScope(QgsExpressionContextUtils.layerScope(layer))

count = layer.featureCount()
step = 100.0 / count if count else 1

request = QgsFeatureRequest(qExp, context)

for current, f in enumerate(layer.getFeatures(request)):
writer.addFeature(f)
progress.setPercentage(int(current * step))

del writer
3 python/plugins/processing/algs/qgis/QGISAlgorithmProvider.py
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@@ -55,6 +55,7 @@
from .RandomExtract import RandomExtract
from .RandomExtractWithinSubsets import RandomExtractWithinSubsets
from .ExtractByLocation import ExtractByLocation
from .ExtractByExpression import ExtractByExpression
from .PointsInPolygon import PointsInPolygon
from .PointsInPolygonUnique import PointsInPolygonUnique
from .PointsInPolygonWeighted import PointsInPolygonWeighted
@@ -192,7 +193,7 @@ def __init__(self):
ZonalStatistics(), PointsFromPolygons(),
PointsFromLines(), RandomPointsExtent(),
RandomPointsLayer(), RandomPointsPolygonsFixed(),
RandomPointsPolygonsVariable(),
RandomPointsPolygonsVariable(), ExtractByExpression(),
RandomPointsAlongLines(), PointsToPaths(),
PostGISExecuteSQL(), ImportIntoPostGIS(),
SetVectorStyle(), SetRasterStyle(),
30 python/plugins/processing/tests/testdata/expected/extract_expression.gml
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@@ -0,0 +1,30 @@
<?xml version="1.0" encoding="utf-8" ?>
<ogr:FeatureCollection
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://ogr.maptools.org/ extract_expression.xsd"
xmlns:ogr="http://ogr.maptools.org/"
xmlns:gml="http://www.opengis.net/gml">
<gml:boundedBy>
<gml:Box>
<gml:coord><gml:X>4</gml:X><gml:Y>-3</gml:Y></gml:coord>
<gml:coord><gml:X>10</gml:X><gml:Y>5</gml:Y></gml:coord>
</gml:Box>
</gml:boundedBy>

<gml:featureMember>
<ogr:extract_expression fid="polys.1">
<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>
<ogr:name>Aaaaa</ogr:name>
<ogr:intval>-33</ogr:intval>
<ogr:floatval>0.00000</ogr:floatval>
</ogr:extract_expression>
</gml:featureMember>
<gml:featureMember>
<ogr:extract_expression fid="polys.3">
<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>
<ogr:name>ASDF</ogr:name>
<ogr:intval>0</ogr:intval>
<ogr:floatval xsi:nil="true"/>
</ogr:extract_expression>
</gml:featureMember>
</ogr:FeatureCollection>
45 python/plugins/processing/tests/testdata/expected/extract_expression.xsd
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@@ -0,0 +1,45 @@
<?xml version="1.0" encoding="UTF-8"?>
<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">
<xs:import namespace="http://www.opengis.net/gml" schemaLocation="http://schemas.opengis.net/gml/2.1.2/feature.xsd"/>
<xs:element name="FeatureCollection" type="ogr:FeatureCollectionType" substitutionGroup="gml:_FeatureCollection"/>
<xs:complexType name="FeatureCollectionType">
<xs:complexContent>
<xs:extension base="gml:AbstractFeatureCollectionType">
<xs:attribute name="lockId" type="xs:string" use="optional"/>
<xs:attribute name="scope" type="xs:string" use="optional"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:element name="extract_expression" type="ogr:extract_expression_Type" substitutionGroup="gml:_Feature"/>
<xs:complexType name="extract_expression_Type">
<xs:complexContent>
<xs:extension base="gml:AbstractFeatureType">
<xs:sequence>
<xs:element name="geometryProperty" type="gml:PolygonPropertyType" nillable="true" minOccurs="0" maxOccurs="1"/>
<xs:element name="name" nillable="true" minOccurs="0" maxOccurs="1">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:maxLength value="255"/>
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name="intval" nillable="true" minOccurs="0" maxOccurs="1">
<xs:simpleType>
<xs:restriction base="xs:integer">
<xs:totalDigits value="10"/>
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name="floatval" nillable="true" minOccurs="0" maxOccurs="1">
<xs:simpleType>
<xs:restriction base="xs:decimal">
<xs:totalDigits value="21"/>
<xs:fractionDigits value="5"/>
</xs:restriction>
</xs:simpleType>
</xs:element>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
</xs:schema>
12 python/plugins/processing/tests/testdata/qgis_algorithm_tests.yaml
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@@ -614,3 +614,15 @@ tests:
OUTPUT:
name: expected/single_to_multi.gml
type: vector

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

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