QGIS/python/plugins/processing/algs/qgis/RandomSelectionWithinSubsets.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 os
import random

from qgis.PyQt.QtGui import QIcon

from qgis.core import (
    QgsApplication,
    QgsFeatureRequest,
    QgsProcessingException,
    QgsProcessingUtils,
    QgsProcessingAlgorithm,
    QgsProcessingParameterVectorLayer,
    QgsProcessingParameterEnum,
    QgsProcessingParameterField,
    QgsProcessingParameterNumber,
    QgsProcessingParameterFeatureSink,
    QgsProcessingOutputVectorLayer,
)
from collections import defaultdict
from processing.algs.qgis.QgisAlgorithm import QgisAlgorithm

pluginPath = os.path.split(os.path.split(os.path.dirname(__file__))[0])[0]


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

    def icon(self):
        return QgsApplication.getThemeIcon("/algorithms/mAlgorithmSelectRandom.svg")

    def svgIconPath(self):
        return QgsApplication.iconPath("/algorithms/mAlgorithmSelectRandom.svg")

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

    def groupId(self):
        return "vectorselection"

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

    def flags(self):
        return (
            super().flags()
            | QgsProcessingAlgorithm.Flag.FlagNoThreading
            | QgsProcessingAlgorithm.Flag.FlagNotAvailableInStandaloneTool
        )

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

        self.addParameter(
            QgsProcessingParameterVectorLayer(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.addOutput(
            QgsProcessingOutputVectorLayer(
                self.OUTPUT, self.tr("Selected (stratified random)")
            )
        )

    def name(self):
        return "randomselectionwithinsubsets"

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

    def processAlgorithm(self, parameters, context, feedback):
        layer = self.parameterAsVectorLayer(parameters, self.INPUT, context)
        method = self.parameterAsEnum(parameters, self.METHOD, context)
        field = self.parameterAsString(parameters, self.FIELD, context)

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

        unique = layer.uniqueValues(index)
        featureCount = layer.featureCount()

        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 a "
                        "different value and try again."
                    )
                )
            value = value / 100.0

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

        if len(unique) != featureCount:
            classes = defaultdict(list)

            features = layer.getFeatures(
                QgsFeatureRequest()
                .setFlags(QgsFeatureRequest.Flag.NoGeometry)
                .setSubsetOfAttributes([index])
            )

            for i, feature in enumerate(features):
                if feedback.isCanceled():
                    break

                classes[feature[index]].append(feature.id())
                feedback.setProgress(int(i * total))

            selran = []
            for k, subset in classes.items():
                if feedback.isCanceled():
                    break

                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))

            layer.selectByIds(selran)
        else:
            layer.selectByIds(
                list(range(featureCount))
            )  # FIXME: implies continuous feature ids

        return {self.OUTPUT: parameters[self.INPUT]}