QGIS/python/plugins/processing/algs/qgis/RandomExtractWithinSubsets.py

"""
***************************************************************************
    RandomSelectionWithinSubsets.py
    ---------------------
    Date                 : August 2012
    Copyright            : (C) 2012 by Victor Olaya
    Email                : volayaf 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__ = "Victor Olaya"
__date__ = "August 2012"
__copyright__ = "(C) 2012, Victor Olaya"

import random

from qgis.core import (
    QgsFeatureSink,
    QgsProcessingException,
    QgsProcessingParameterFeatureSource,
    QgsProcessingParameterEnum,
    QgsProcessingParameterField,
    QgsProcessingParameterNumber,
    QgsProcessingParameterFeatureSink,
    QgsProcessingFeatureSource,
    QgsFeatureRequest,
)
from collections import defaultdict
from processing.algs.qgis.QgisAlgorithm import QgisAlgorithm


class RandomExtractWithinSubsets(QgisAlgorithm):
    INPUT = "INPUT"
    METHOD = "METHOD"
    NUMBER = "NUMBER"
    FIELD = "FIELD"
    OUTPUT = "OUTPUT"

    def group(self):
        return self.tr("Vector selection")

    def groupId(self):
        return "vectorselection"

    def __init__(self):
        super().__init__()

    def initAlgorithm(self, config=None):
        self.methods = [
            self.tr("Number of selected features"),
            self.tr("Percentage of selected features"),
        ]

        self.addParameter(
            QgsProcessingParameterFeatureSource(self.INPUT, self.tr("Input layer"))
        )

        self.addParameter(
            QgsProcessingParameterField(
                self.FIELD, self.tr("ID field"), None, self.INPUT
            )
        )

        self.addParameter(
            QgsProcessingParameterEnum(
                self.METHOD, self.tr("Method"), self.methods, False, 0
            )
        )

        self.addParameter(
            QgsProcessingParameterNumber(
                self.NUMBER,
                self.tr("Number/percentage of selected features"),
                QgsProcessingParameterNumber.Type.Integer,
                10,
                False,
                0.0,
            )
        )

        self.addParameter(
            QgsProcessingParameterFeatureSink(
                self.OUTPUT, self.tr("Extracted (random stratified)")
            )
        )

    def name(self):
        return "randomextractwithinsubsets"

    def displayName(self):
        return self.tr("Random extract within subsets")

    def processAlgorithm(self, parameters, context, feedback):
        source = self.parameterAsSource(parameters, self.INPUT, context)
        if source is None:
            raise QgsProcessingException(
                self.invalidSourceError(parameters, self.INPUT)
            )

        method = self.parameterAsEnum(parameters, self.METHOD, context)

        field = self.parameterAsString(parameters, self.FIELD, context)

        index = source.fields().lookupField(field)

        features = source.getFeatures(
            QgsFeatureRequest(),
            QgsProcessingFeatureSource.Flag.FlagSkipGeometryValidityChecks,
        )
        featureCount = source.featureCount()
        unique = source.uniqueValues(index)
        value = self.parameterAsInt(parameters, self.NUMBER, context)
        if method == 0:
            if value > featureCount:
                raise QgsProcessingException(
                    self.tr(
                        "Selected number is greater that feature count. "
                        "Choose lesser value and try again."
                    )
                )
        else:
            if value > 100:
                raise QgsProcessingException(
                    self.tr(
                        "Percentage can't be greater than 100. Set "
                        "correct value and try again."
                    )
                )
            value = value / 100.0

        (sink, dest_id) = self.parameterAsSink(
            parameters,
            self.OUTPUT,
            context,
            source.fields(),
            source.wkbType(),
            source.sourceCrs(),
        )
        if sink is None:
            raise QgsProcessingException(self.invalidSinkError(parameters, self.OUTPUT))

        selran = []
        total = 100.0 / (featureCount * len(unique)) if featureCount else 1

        classes = defaultdict(list)
        for i, feature in enumerate(features):
            if feedback.isCanceled():
                break
            attrs = feature.attributes()
            classes[attrs[index]].append(feature)
            feedback.setProgress(int(i * total))

        for k, subset in classes.items():
            selValue = value if method != 1 else int(round(value * len(subset), 0))
            if selValue > len(subset):
                selValue = len(subset)
                feedback.reportError(
                    self.tr(
                        'Subset "{}" is smaller than requested number of features.'
                    ).format(k)
                )
            selran.extend(random.sample(subset, selValue))

        total = 100.0 / featureCount if featureCount else 1
        for i, feat in enumerate(selran):
            if feedback.isCanceled():
                break
            sink.addFeature(feat, QgsFeatureSink.Flag.FastInsert)
            feedback.setProgress(int(i * total))
        sink.finalize()
        return {self.OUTPUT: dest_id}