Java tutorial
/* * 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.solr.client.solrj.io.eval; import java.io.IOException; import java.math.BigDecimal; import java.util.List; import java.util.Locale; import org.apache.commons.math3.stat.StatUtils; import org.apache.solr.client.solrj.io.stream.expr.StreamExpression; import org.apache.solr.client.solrj.io.stream.expr.StreamFactory; public class MeanDifferenceEvaluator extends RecursiveNumericEvaluator implements TwoValueWorker { protected static final long serialVersionUID = 1L; public MeanDifferenceEvaluator(StreamExpression expression, StreamFactory factory) throws IOException { super(expression, factory); } @Override public Object doWork(Object first, Object second) throws IOException { if (null == first) { throw new IOException(String.format(Locale.ROOT, "Invalid expression %s - null found for the first value", toExpression(constructingFactory))); } if (null == second) { throw new IOException(String.format(Locale.ROOT, "Invalid expression %s - null found for the second value", toExpression(constructingFactory))); } if (!(first instanceof List<?>)) { throw new IOException(String.format(Locale.ROOT, "Invalid expression %s - found type %s for the first value, expecting a list of numbers", toExpression(constructingFactory), first.getClass().getSimpleName())); } if (!(second instanceof List<?>)) { throw new IOException(String.format(Locale.ROOT, "Invalid expression %s - found type %s for the second value, expecting a list of numbers", toExpression(constructingFactory), first.getClass().getSimpleName())); } return StatUtils.meanDifference( ((List) first).stream().mapToDouble(value -> ((BigDecimal) value).doubleValue()).toArray(), ((List) second).stream().mapToDouble(value -> ((BigDecimal) value).doubleValue()).toArray()); } }