/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.jena.sparql.expr.aggregate.lib;
import org.apache.jena.sparql.engine.binding.Binding ;
import org.apache.jena.sparql.expr.Expr ;
import org.apache.jena.sparql.expr.ExprEvalException ;
import org.apache.jena.sparql.expr.NodeValue ;
import org.apache.jena.sparql.expr.aggregate.AccumulatorExpr ;
import org.apache.jena.sparql.function.FunctionEnv ;
/** Base for statistics aggregations */
abstract class AccStatBase extends AccumulatorExpr {
// Could also be used for AVG and SUM but those came before this.
private static final NodeValue noValuesToAvg = NodeValue.nvZERO ; // null? NaN?
private static final NodeValue errorValue = null ;
public AccStatBase(Expr expr, boolean distinct) {
// Merge "distinct" into AccumulatorExpr
super(expr, distinct);
}
protected long count = 0 ;
protected double K = 0 ;
// https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance
// Var = (SumSq − (Sum × Sum) / n) / (n − 1)
// These are offset by K.
protected double sum = 0 ;
protected double sumSquared = 0 ;
@Override
final protected NodeValue getAccValue() {
if ( super.errorCount != 0 )
//throw new ExprEvalException("avg: error in group") ;
return null ;
if ( count <= 0 ) return noValuesToAvg ;
try {
double x1 = calc() ;
return NodeValue.makeDouble(x1) ;
} catch (ExprEvalException ex) { return errorValue ; }
}
abstract protected double calc() ;
/** Calculate the variance (sample) */
final protected double calcVarianceSample() {
// (N*sum(?x*?x) - sum(?x) ) / N*(N-1)
return AccStatLib.calcVarianceSample(sumSquared, sum, count) ;
}
/** Calculate the variance (population) */
final protected double calcVariancePop() {
// (N*sum(?x*?x) - sum(?x) ) / N*N
return AccStatLib.calcVariancePopulation(sumSquared, sum, count) ;
}
@Override
protected void accumulate(NodeValue nv, Binding binding, FunctionEnv functionEnv) {
// shifted_data_variance
if ( nv.isNumber() ) {
double d = nv.getDouble() ;
count++ ;
if ( count == 1 ) {
K = d ;
sum = (d-K) ; // == 0 of K set.
sumSquared = (d-K)*(d-K) ; // == 0
return ;
}
else {
double dk = (d-K) ;
double dk2 = dk * dk ;
sum = sum + dk ;
sumSquared = sumSquared + dk2 ;
}
}
else
throw new ExprEvalException("Not a number: "+nv) ;
}
@Override
protected void accumulateError(Binding binding, FunctionEnv functionEnv)
{}
}