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

# -*- coding: utf-8 -*-

"""
***************************************************************************
    RandomSelection.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'

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

__revision__ = '$Format:%H$'

import random

from PyQt4.QtCore import *
from qgis.core import *

from processing.core.GeoAlgorithm import GeoAlgorithm
from processing.core.GeoAlgorithmExecutionException import \
        GeoAlgorithmExecutionException
from processing.core.parameters import ParameterSelection
from processing.core.parameters import ParameterVector
from processing.core.parameters import ParameterNumber
from processing.core.outputs import OutputVector
from processing.tools import dataobjects


class RandomSelection(GeoAlgorithm):

    INPUT = 'INPUT'
    OUTPUT = 'OUTPUT'
    METHOD = 'METHOD'
    NUMBER = 'NUMBER'

    METHODS = ['Number of selected features',
               'Percentage of selected features']
    def defineCharacteristics(self):
        self.allowOnlyOpenedLayers = True
        self.name = 'Random selection'
        self.group = 'Vector selection 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/percentage of selected features', 0, None,
                          10))
        self.addOutput(OutputVector(self.OUTPUT, 'Selection', True))

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

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

        layer.removeSelection()

        if method == 0:
            if value > featureCount:
                raise GeoAlgorithmExecutionException(
                        'Selected number is greater than feature count. \
                        Choose a lower value and try again.')
        else:
            if value > 100:
                raise GeoAlgorithmExecutionException(
                        "Percentage can't be greater than 100. Set a \
                        different 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)