[GitHub] [iceberg] amogh-jahagirdar commented on a diff in pull request #6405: API: Add Aggregate expression evaluation

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

amogh-jahagirdar commented on code in PR #6405:
URL: https://github.com/apache/iceberg/pull/6405#discussion_r1046618283


##########
api/src/main/java/org/apache/iceberg/expressions/CountStar.java:
##########
@@ -0,0 +1,44 @@
+/*
+ * 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.iceberg.expressions;
+
+import org.apache.iceberg.DataFile;
+import org.apache.iceberg.StructLike;
+
+public class CountStar<T> extends CountAggregate<T> {
+  protected CountStar(BoundTerm<T> term) {
+    super(Operation.COUNT_STAR, term);
+  }
+
+  @Override
+  protected Long countFor(StructLike row) {
+    return 1L;
+  }
+
+  @Override
+  protected Long countFor(DataFile file) {
+    long count = file.recordCount();
+    if (count < 0) {
+      return null;
+    }

Review Comment:
   Curious when would this ever be negative? or is this just for this logic to be defensive against bad metadata? 



##########
api/src/main/java/org/apache/iceberg/expressions/AggregateEvaluator.java:
##########
@@ -0,0 +1,110 @@
+/*
+ * 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.iceberg.expressions;
+
+import java.util.List;
+import java.util.stream.Collectors;
+import org.apache.iceberg.DataFile;
+import org.apache.iceberg.Schema;
+import org.apache.iceberg.StructLike;
+import org.apache.iceberg.relocated.com.google.common.collect.ImmutableList;
+import org.apache.iceberg.relocated.com.google.common.collect.Lists;
+import org.apache.iceberg.types.Types;
+
+public class AggregateEvaluator {
+  public static AggregateEvaluator create(Schema schema, Expression... aggregates) {
+    return create(schema, aggregates);
+  }
+
+  public static AggregateEvaluator create(Schema schema, List<Expression> aggregates) {
+    return create(schema.asStruct(), aggregates);
+  }
+
+  private static AggregateEvaluator create(Types.StructType struct, List<Expression> aggregates) {
+    List<BoundAggregate<?, ?>> boundAggregates =
+        aggregates.stream()
+            .map(expr -> Binder.bind(struct, expr))
+            .map(bound -> (BoundAggregate<?, ?>) bound)
+            .collect(Collectors.toList());
+
+    return new AggregateEvaluator(boundAggregates);
+  }
+
+  private final List<BoundAggregate.Aggregator<?>> aggregators;
+  private final Types.StructType resultType;
+
+  private AggregateEvaluator(List<BoundAggregate<?, ?>> aggregates) {
+    ImmutableList.Builder<BoundAggregate.Aggregator<?>> aggregatorsBuilder =
+        ImmutableList.builder();
+    List<Types.NestedField> resultFields = Lists.newArrayList();
+    for (int pos = 0; pos < aggregates.size(); pos += 1) {
+      BoundAggregate<?, ?> aggregate = aggregates.get(pos);
+      aggregatorsBuilder.add(aggregates.get(pos).newAggregator());

Review Comment:
   I guess here we could also reuse `aggregate`?



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