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https://issues.apache.org/jira/browse/DRILL-7096?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16914408#comment-16914408
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ASF GitHub Bot commented on DRILL-7096:
---------------------------------------
vvysotskyi commented on pull request #1829: DRILL-7096: Develop vector for
canonical Map<K,V>
URL: https://github.com/apache/drill/pull/1829#discussion_r317194671
##########
File path:
exec/vector/src/main/java/org/apache/drill/exec/vector/complex/DictVector.java
##########
@@ -0,0 +1,321 @@
+/*
+ * 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.drill.exec.vector.complex;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+
+import org.apache.drill.common.exceptions.DrillRuntimeException;
+import org.apache.drill.common.types.TypeProtos.MajorType;
+import org.apache.drill.common.types.TypeProtos.MinorType;
+import org.apache.drill.common.types.Types;
+import org.apache.drill.exec.expr.holders.RepeatedValueHolder;
+import org.apache.drill.exec.expr.holders.DictHolder;
+import org.apache.drill.exec.memory.BufferAllocator;
+import org.apache.drill.exec.record.MaterializedField;
+import org.apache.drill.exec.record.TransferPair;
+import org.apache.drill.exec.util.CallBack;
+import org.apache.drill.exec.util.JsonStringHashMap;
+import org.apache.drill.exec.vector.ValueVector;
+import org.apache.drill.exec.vector.complex.impl.SingleDictReaderImpl;
+
+/**
+ * A {@link ValueVector} holding key-value pairs.
+ * <p>This vector is essentially a {@link RepeatedMapVector} but with
constraints:
+ * it may have 2 children only, named {@link #FIELD_KEY_NAME} and {@link
#FIELD_VALUE_NAME}.
+ * The {@link #FIELD_KEY_NAME} can be of primitive type only and its values
should not be {@code null},
+ * while the other, {@link #FIELD_VALUE_NAME}, field can be either of
primitive or complex type.
+ *
+ * <p>This vector has it's own {@link
org.apache.drill.exec.vector.complex.reader.FieldReader} and
+ * {@link org.apache.drill.exec.vector.complex.writer.FieldWriter} to ensure
data is read and written correctly.
+ * In addition, the reader is responsible for getting a value for a given key.
+ *
+ * <p>Additionally, {@code Object} representation is changed in {@link
Accessor#getObject(int)}
+ * to represent it as {@link JsonStringHashMap} with appropriate {@code key}
and {@code value} types.
+ *
+ * <p>(The structure corresponds to Java's notion of {@link Map}).
+ *
+ * @see SingleDictReaderImpl reader corresponding to the vector
+ * @see org.apache.drill.exec.vector.complex.impl.SingleDictWriter writer
corresponding to the vector
+ */
+public final class DictVector extends AbstractRepeatedMapVector {
+
+ public final static MajorType TYPE = Types.optional(MinorType.DICT);
+
+ public static final String FIELD_KEY_NAME = "key";
+ public static final String FIELD_VALUE_NAME = "value";
+ public static final List<String> fieldNames =
Collections.unmodifiableList(Arrays.asList(FIELD_KEY_NAME, FIELD_VALUE_NAME));
Review comment:
There is no need to wrap `Arrays.asList`
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> Develop vector for canonical Map<K,V>
> -------------------------------------
>
> Key: DRILL-7096
> URL: https://issues.apache.org/jira/browse/DRILL-7096
> Project: Apache Drill
> Issue Type: Sub-task
> Reporter: Igor Guzenko
> Assignee: Bohdan Kazydub
> Priority: Major
> Fix For: 1.17.0
>
>
> Canonical Map<K,V> datatype can be represented using combination of three
> value vectors:
> keysVector - vector for storing keys of each map
> valuesVector - vector for storing values of each map
> offsetsVector - vector for storing of start indexes of next each map
> So it's not very hard to create such Map vector, but there is a major issue
> with such map representation. It's hard to search maps values by key in such
> vector, need to investigate some advanced techniques to make such search
> efficient. Or find other more suitable options to represent map datatype in
> world of vectors.
> After question about maps, Apache Arrow developers responded that for Java
> they don't have real Map vector, for now they just have logical Map type
> definition where they define Map like: List< Struct<key:key_type,
> value:value_type> >. So implementation of value vector would be useful for
> Arrow too.
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