[GitHub] [jena] rvesse commented on a change in pull request #568: Add Aggregate Median to SPARQL ARQ syntax

[GitBox <gi...@apache.org>]

rvesse commented on a change in pull request #568: Add Aggregate Median to SPARQL ARQ syntax
URL: https://github.com/apache/jena/pull/568#discussion_r284659933
 
 

 ##########
 File path: jena-arq/src/main/java/org/apache/jena/sparql/expr/aggregate/AggMedian.java
 ##########
 @@ -0,0 +1,123 @@
+/*
+ * 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;
+
+import java.lang.reflect.Array;
+import java.util.ArrayList;
+
+import org.apache.commons.math3.stat.descriptive.rank.Median;
+import org.apache.jena.graph.Node ;
+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.ExprList ;
+import org.apache.jena.sparql.expr.NodeValue ;
+import org.apache.jena.sparql.expr.nodevalue.XSDFuncOp ;
+import org.apache.jena.sparql.function.FunctionEnv ;
+
+public class AggMedian extends AggregatorBase
+{
+    // ---- MEDIAN(?var)
+    public AggMedian(Expr expr) { super("MEDIAN", false, expr) ; } 
+    @Override
+    public Aggregator copy(ExprList expr) { return new AggMedian(expr.get(0)) ; }
+
+    // XQuery/XPath Functions&Operators suggests zero
+    // SQL suggests null.
+    private static final NodeValue noValuesToMedian = NodeValue.nvZERO ; // null 
+
+    @Override
+    public Accumulator createAccumulator()
+    { 
+        return new AccMedian(getExpr()) ;
+    }
+
+    @Override
+    public Node getValueEmpty()     { return NodeValue.toNode(noValuesToMedian) ; } 
+    
+    @Override
+    public int hashCode()   { return HC_AggMedian ^ getExprList().hashCode() ; }
+
+    @Override
+    public boolean equals(Aggregator other, boolean bySyntax) {
+        if ( other == null ) return false ;
+        if ( this == other ) return true ;
+        if ( ! ( other instanceof AggMedian ) ) return false ;
+        AggMedian a = (AggMedian)other ;
+        return exprList.equals(a.exprList, bySyntax) ;
+    }
+    
+    // ---- Accumulator
+    private static class AccMedian extends AccumulatorExpr
+    {
+        // Non-empty case but still can be nothing because the expression may be undefined.
+        private NodeValue total = noValuesToMedian ;
+        private int count = 0 ;
+        ArrayList<NodeValue> collection=new ArrayList<NodeValue>(); 
+        
+        static final boolean DEBUG = false ;
+        
+        public AccMedian(Expr expr) { super(expr, false) ; }
+
+        @Override
+        protected void accumulate(NodeValue nv, Binding binding, FunctionEnv functionEnv)
+        { 
+            if ( DEBUG ) System.out.println("median: "+nv) ;
+
+            if ( nv.isNumber() )
+            {
+                count++ ;
+                if ( total == noValuesToMedian )
+                    total = nv ;
+                else
+                    total = XSDFuncOp.numAdd(nv, total) ;
+                	collection.add(nv);
+            }
+            else
+            {
+                //ARQ.getExecLogger().warn("Evaluation error: median() on "+nv) ;
+                throw new ExprEvalException("median: not a number: "+nv) ;
+            }
+            
+            if ( DEBUG ) System.out.println("median: ("+total+","+count+")") ;
+        }
+        
+        @Override
+        protected void accumulateError(Binding binding, FunctionEnv functionEnv)
+        {}
+
+        @Override
+        public NodeValue getAccValue()
+        {
+            if ( count == 0 ) return noValuesToMedian ;
+            if ( super.errorCount != 0 )
+                //throw new ExprEvalException("median: error in group") ; 
+                return null ;
+            //NodeValue nvCount = NodeValue.makeInteger(count) ;
+                        
+            double[] arrDouble = new double[collection.size()];
+            for(int i=0; i<collection.size(); i++){
+            	arrDouble[i] = Double.parseDouble(collection.get(i).toString());
 
 Review comment:
   Can use `NodeValue.getDouble()` here as the value will already have been parsed

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