QGIS/python/plugins/sextante/ftools/RandomSelection.py

import os.path
import random

from PyQt4 import QtGui
from PyQt4.QtCore import *

from qgis.core import *

from sextante.core.GeoAlgorithm import GeoAlgorithm
from sextante.core.GeoAlgorithmExecutionException import GeoAlgorithmExecutionException
from sextante.core.QGisLayers import QGisLayers

from sextante.parameters.ParameterSelection import ParameterSelection
from sextante.parameters.ParameterVector import ParameterVector
from sextante.parameters.ParameterNumber import ParameterNumber

from sextante.outputs.OutputVector import OutputVector

class RandomSelection(GeoAlgorithm):

    INPUT = "INPUT"
    OUTPUT = "OUTPUT"
    METHOD = "METHOD"
    NUMBER = "NUMBER"

    METHODS = ["Number of selected features",
               "Percentage of selected features"
              ]

    def getIcon(self):
        return QtGui.QIcon(os.path.dirname(__file__) + "/icons/random_selection.png")

    def defineCharacteristics(self):
        self.name = "Random selection"
        self.group = "Research tools"

        self.addParameter(ParameterVector(self.INPUT, "Input layer", ParameterVector.VECTOR_TYPE_ANY))
        self.addParameter(ParameterSelection(self.METHOD, "Method", self.METHODS, 0))
        self.addParameter(ParameterNumber(self.NUMBER, "Number/persentage of selected features", 1, None, 10))
        self.addOutput(OutputVector(self.OUTPUT, "Selection", True))

    def processAlgorithm(self, progress):
        filename = self.getParameterValue(self.INPUT)
        layer = QGisLayers.getObjectFromUri(filename)
        method = self.getParameterValue(self.METHOD)

        featureCount = layer.featureCount()

        value = int(self.getParameterValue(self.NUMBER))

        if method == 0:
            if value > featureCount:
                raise GeoAlgorithmExecutionException("Selected number is greater that feature count. Choose lesser value and try again.")
        else:
            if value > 100:
                raise GeoAlgorithmExecutionException("Persentage can't be greater than 100. Set corrent value and try again.")
            value = int(round((value / 100.0000), 4) * featureCount)

        selran = random.sample(xrange(0, featureCount), value)

        layer.setSelectedFeatures(selran)
        self.setOutputValue(self.OUTPUT, filename)