Github user mengxr commented on a diff in the pull request:
https://github.com/apache/spark/pull/11108#discussion_r56434392
--- Diff:
examples/src/main/java/org/apache/spark/examples/mllib/JavaStratifiedSamplingExample.java
---
@@ -0,0 +1,81 @@
+/*
+ * 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.spark.examples.mllib;
+
+import org.apache.spark.SparkConf;
+import org.apache.spark.api.java.JavaSparkContext;
+
+// $example on$
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import scala.Tuple2;
+
+import org.apache.spark.api.java.JavaPairRDD;
+import org.apache.spark.api.java.function.VoidFunction;
+// $example off$
+
+public class JavaStratifiedSamplingExample {
+ public static void main(String[] args) {
+
+ SparkConf conf = new
SparkConf().setAppName("JavaStratifiedSamplingExample");
+ JavaSparkContext jsc = new JavaSparkContext(conf);
+
+ // $example on$
+ List<Tuple2<Integer, Character>> list = new ArrayList<>();
+ list.add(new Tuple2(1, 'a'));
+ list.add(new Tuple2(1, 'b'));
+ list.add(new Tuple2(2, 'c'));
+ list.add(new Tuple2(2, 'd'));
+ list.add(new Tuple2(2, 'e'));
+ list.add(new Tuple2(3, 'f'));
+
+ // an RDD of any key value pairs JavaPairRDD<K, V>
+ JavaPairRDD<Integer, Character> data = jsc.parallelizePairs(list);
+
+ // specify the exact fraction desired from each key Map<K, Object>
+ Map<Integer, Object> fractions = new HashMap<>();
+
+ fractions.put(1, 0.1);
+ fractions.put(2, 0.6);
+ fractions.put(3, 0.3);
+
+ // Get an exact sample from each stratum
+ JavaPairRDD<Integer, Character> approxSample =
+ data.sampleByKey(false, fractions); // JavaPairRDD<K, V>
+ JavaPairRDD<Integer, Character> exactSample =
+ data.sampleByKeyExact(false, fractions); // JavaPairRDD<K, V>
+ // $example off$
+
+ approxSample.foreach(new VoidFunction<Tuple2<Integer, Character>>() {
--- End diff --
* Okay, I see why we don't want to have `println` lines in the example now.
If it is just one line of code, I prefer putting it inside the example.
* This won't work on a distributed server. We need to collect them first.
~~~java
for(Tuple2<Integer, Character> t: approxSample.collect()) {
...
}
~~~
Please also try saving some type info by using `<>` if feasible.
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