[HIVEMALL-220] Implement Cofactor

core/src/main/java/hivemall/factorization/cofactor/CofactorizationPredictUDF.java

@@ -0,0 +1,78 @@
+/*
+ * 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 hivemall.factorization.cofactor;
+
+import java.util.List;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+import org.apache.hadoop.hive.ql.exec.Description;
+import org.apache.hadoop.hive.ql.exec.UDF;
+import org.apache.hadoop.hive.ql.metadata.HiveException;
+import org.apache.hadoop.hive.ql.udf.UDFType;
+import org.apache.hadoop.hive.serde2.io.DoubleWritable;
+import org.apache.hadoop.io.FloatWritable;
+
+@Description(name = "cofactor_predict",
+        value = "_FUNC_(array<float> theta, array<float> beta) - Returns the prediction value")
+@UDFType(deterministic = true, stateful = false)
+public final class CofactorizationPredictUDF extends UDF {
+
+    private static final DoubleWritable ZERO = new DoubleWritable(0.d);
+
+    // reused result variable
+    private final DoubleWritable result = new DoubleWritable();
+
+    @Nonnull
+    public DoubleWritable evaluate(@Nullable List<FloatWritable> Pu,
+            @Nullable List<FloatWritable> Qi) throws HiveException {
+        if (Pu == null || Qi == null) {
+            return ZERO;
+        }
+
+        final int PuSize = Pu.size();
+        final int QiSize = Qi.size();
+        // workaround for TD
+        if (PuSize == 0) {
+            return ZERO;
+        } else if (QiSize == 0) {
+            return ZERO;
+        }
+
+        if (QiSize != PuSize) {
+            throw new HiveException("|Pu| " + PuSize + " was not equal to |Qi| " + QiSize);
+        }
+
+        double ret = 0.d;
+        for (int k = 0; k < PuSize; k++) {
+            FloatWritable Pu_k = Pu.get(k);
+            if (Pu_k == null) {
+                continue;
+            }
+            FloatWritable Qi_k = Qi.get(k);
+            if (Qi_k == null) {
+                continue;
+            }
+            ret += Pu_k.get() * Qi_k.get();
+        }
+        result.set(ret);
+        return result;
+    }
+}