davisusanibar commented on code in PR #215:
URL: https://github.com/apache/arrow-cookbook/pull/215#discussion_r880897554
##########
java/source/io.rst:
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@@ -443,3 +443,109 @@ Reading Parquet File
********************
Please check :doc:`Dataset <./dataset>`
+
+Handling Data with Dictionaries
+*******************************
+
+Reading and writing dictionary-encoded data requires separately tracking the
dictionaries.
+
+.. testcode::
+
+ import org.apache.arrow.memory.BufferAllocator;
+ import org.apache.arrow.memory.RootAllocator;
+ import org.apache.arrow.vector.FieldVector;
+ import org.apache.arrow.vector.ValueVector;
+ import org.apache.arrow.vector.VarCharVector;
+ import org.apache.arrow.vector.VectorSchemaRoot;
+ import org.apache.arrow.vector.dictionary.Dictionary;
+ import org.apache.arrow.vector.dictionary.DictionaryEncoder;
+ import org.apache.arrow.vector.dictionary.DictionaryProvider;
+ import org.apache.arrow.vector.ipc.ArrowFileReader;
+ import org.apache.arrow.vector.ipc.ArrowFileWriter;
+ import org.apache.arrow.vector.ipc.message.ArrowBlock;
+ import org.apache.arrow.vector.types.pojo.ArrowType;
+ import org.apache.arrow.vector.types.pojo.DictionaryEncoding;
+
+ import java.io.File;
+ import java.io.FileInputStream;
+ import java.io.FileNotFoundException;
+ import java.io.FileOutputStream;
+ import java.io.IOException;
+ import java.nio.charset.StandardCharsets;
+
+ try (BufferAllocator root = new RootAllocator();
+ VarCharVector countries = new VarCharVector("country-dict", root);
+ VarCharVector appUserCountriesUnencoded = new
VarCharVector("app-use-country-dict", root)
+ ) {
+ countries.allocateNew(10);
+ countries.set(0, "Andorra".getBytes(StandardCharsets.UTF_8));
+ countries.set(1, "Cuba".getBytes(StandardCharsets.UTF_8));
+ countries.set(2, "Grecia".getBytes(StandardCharsets.UTF_8));
+ countries.set(3, "Guinea".getBytes(StandardCharsets.UTF_8));
+ countries.set(4, "Islandia".getBytes(StandardCharsets.UTF_8));
+ countries.set(5, "Malta".getBytes(StandardCharsets.UTF_8));
+ countries.set(6, "Tailandia".getBytes(StandardCharsets.UTF_8));
+ countries.set(7, "Uganda".getBytes(StandardCharsets.UTF_8));
+ countries.set(8, "Yemen".getBytes(StandardCharsets.UTF_8));
+ countries.set(9, "Zambia".getBytes(StandardCharsets.UTF_8));
+ countries.setValueCount(10);
+
+ Dictionary countriesDictionary = new Dictionary(countries,
+ new DictionaryEncoding(/*id=*/123L, /*ordered=*/false,
/*indexType=*/new ArrowType.Int(8, true)));
+ System.out.println("Dictionary: " + countriesDictionary);
+
+ appUserCountriesUnencoded.allocateNew(5);
+ appUserCountriesUnencoded.set(0,
"Andorra".getBytes(StandardCharsets.UTF_8));
+ appUserCountriesUnencoded.set(1,
"Guinea".getBytes(StandardCharsets.UTF_8));
+ appUserCountriesUnencoded.set(2,
"Islandia".getBytes(StandardCharsets.UTF_8));
+ appUserCountriesUnencoded.set(3,
"Malta".getBytes(StandardCharsets.UTF_8));
+ appUserCountriesUnencoded.set(4,
"Uganda".getBytes(StandardCharsets.UTF_8));
+ appUserCountriesUnencoded.setValueCount(5);
+ System.out.println("Unencoded data: " + appUserCountriesUnencoded);
+
+ File file = new File("random_access_file_with_dictionary.arrow");
+ DictionaryProvider.MapDictionaryProvider provider = new
DictionaryProvider.MapDictionaryProvider();
+ provider.put(countriesDictionary);
+ try (FieldVector appUseCountryDictionaryEncoded = (FieldVector)
DictionaryEncoder
+ .encode(appUserCountriesUnencoded, countriesDictionary);
+ VectorSchemaRoot vectorSchemaRoot =
VectorSchemaRoot.of(appUseCountryDictionaryEncoded);
+ FileOutputStream fileOutputStream = new FileOutputStream(file);
+ ArrowFileWriter writer = new ArrowFileWriter(vectorSchemaRoot,
provider, fileOutputStream.getChannel())
+ ) {
+ System.out.println("Dictionary-encoded data: "
+appUseCountryDictionaryEncoded);
+ writer.start();
+ writer.writeBatch();
+ writer.end();
+ System.out.println("Record batches written: " +
writer.getRecordBlocks().size() + ". Number of rows written: " +
vectorSchemaRoot.getRowCount());
+ try(
+ BufferAllocator rootAllocator = new RootAllocator();
+ FileInputStream fileInputStream = new
FileInputStream(file);
+ ArrowFileReader reader = new
ArrowFileReader(fileInputStream.getChannel(), rootAllocator)
+ ){
+ for (ArrowBlock arrowBlock : reader.getRecordBlocks()) {
+ reader.loadRecordBatch(arrowBlock);
+ FieldVector appUseCountryDictionaryEncodedRead =
reader.getVectorSchemaRoot().getVector("app-use-country-dict");
+ Dictionary appUseCountryDictionaryRead =
reader.getDictionaryVectors().get(123L);
Review Comment:
We could consider link `getValueCount` or another but it will be weak link.
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