/*
* GeoTools - The Open Source Java GIS Toolkit
* http://geotools.org
*
* (C) 2004-2008, Open Source Geospatial Foundation (OSGeo)
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation;
* version 2.1 of the License.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* Created on May 11, 2005, 6:21 PM
*/
package org.geotools.filter.function;
import java.io.IOException;
import java.util.Collections;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;
import org.geotools.feature.FeatureCollection;
import org.geotools.feature.visitor.AverageVisitor;
import org.geotools.feature.visitor.CalcResult;
import org.geotools.filter.AttributeExpression;
import org.geotools.filter.Expression;
import org.geotools.filter.FunctionExpressionImpl;
import org.geotools.filter.IllegalFilterException;
import org.geotools.filter.visitor.AbstractFilterVisitor;
import org.opengis.feature.Feature;
import org.opengis.feature.simple.SimpleFeature;
import org.opengis.feature.simple.SimpleFeatureType;
import org.opengis.feature.type.FeatureType;
/**
* Calculates the average value of an attribute for a given FeatureCollection
* and Expression.
*
* @author Cory Horner
* @since 2.2M2
* @source $URL$
*/
public class Collection_AverageFunction extends FunctionExpressionImpl {
/** The logger for the filter module. */
private static final Logger LOGGER = org.geotools.util.logging.Logging.getLogger(
"org.geotools.filter.function");
FeatureCollection<FeatureType, Feature> previousFeatureCollection = null;
Object average = null;
Expression expr;
/**
* Creates a new instance of Collection_AverageFunction
*/
public Collection_AverageFunction() {
super("Collection_Average");
}
public int getArgCount() {
return 1;
}
/**
* Calculate average (using FeatureCalc) - only one parameter is used.
*
* @param collection collection to calculate the average
* @param expression Single Expression argument
*
* @return An object containing the average value of the attributes
*
* @throws IllegalFilterException
* @throws IOException
*/
static CalcResult calculateAverage(FeatureCollection<? extends FeatureType, ? extends Feature> collection,
Expression expression) throws IllegalFilterException, IOException {
AverageVisitor averageVisitor = new AverageVisitor(expression);
collection.accepts(averageVisitor, null);
return averageVisitor.getResult();
}
/**
* The provided arguments are evaulated with respect to the
* FeatureCollection.
*
* <p>
* For an aggregate function (like average) please use the WFS mandated XPath
* syntax to refer to featureMember content.
* </p>
*
* <p>
* To refer to all 'X': <code>featureMember/asterisk/X</code>
* </p>
*
* @param args DOCUMENT ME!
*
* @throws IllegalArgumentException DOCUMENT ME!
*/
public void setParameters(List params){
super.setParameters(params);
if (params.size() != 1) {
throw new IllegalArgumentException(
"Require a single argument for average");
}
//HACK: remove cast once completely moved to GeoAPI
expr = (Expression)getExpression(0);
// if we see "featureMembers/*/ATTRIBUTE" change to "ATTRIBUTE"
expr.accept(new AbstractFilterVisitor() {
public void visit(AttributeExpression expression) {
String xpath = expression.getAttributePath();
if (xpath.startsWith("featureMembers/*/")) {
xpath = xpath.substring(17);
} else if (xpath.startsWith("featureMember/*/")) {
xpath = xpath.substring(16);
}
try {
expression.setAttributePath(xpath);
} catch (IllegalFilterException e) {
// ignore
}
}
});
}
@SuppressWarnings("unchecked")
public Object evaluate(Object feature) {
if (feature == null) {
return new Integer(0); // no features were visited in the making of this answer
}
FeatureCollection<FeatureType, Feature> featureCollection = (FeatureCollection<FeatureType, Feature>) feature;
synchronized (featureCollection) {
if (featureCollection != previousFeatureCollection) {
previousFeatureCollection = featureCollection;
average = null;
try {
CalcResult result = calculateAverage(featureCollection, expr);
if (result != null) {
average = result.getValue();
}
} catch (IllegalFilterException e) {
LOGGER.log(Level.FINER, e.getLocalizedMessage(), e);
} catch (IOException e) {
LOGGER.log(Level.FINER, e.getLocalizedMessage(), e);
}
}
}
return average;
}
public void setExpression(Expression e) {
setParameters(Collections.singletonList(e));
}
/**
* Return this function as a string.
*
* @return String representation of this average function.
*/
public String toString() {
return "Collection_Average(" + expr + ")";
}
}