Practice2.java

/*
 * Copyright 2016-2017 Leon Chen
 *
 * Licensed 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 cn.nextop.rxjava.share.practices;

import java.util.HashMap;
import java.util.Map;

import cn.nextop.rxjava.share.util.Tuples;
import cn.nextop.rxjava.share.util.type.Tuple2;
import io.reactivex.Observable;
import io.reactivex.Single;

/**
 * @author Baoyi Chen
 */
public class Practice2 {

	/*
	 * 举例: words = Observable["a", "a", "b", "c", "c"] 返回: Observable[("a", 2),
	 * ("b", 1), ("c", 2)]
	 */
	public Observable<Tuple2<String, Integer>> wordCount1(Observable<String> words) {
		return words.groupBy(e -> e).flatMap(e -> e.count().toObservable().map(x -> Tuples.of(e.getKey(), x.intValue())));
	}

	/*
	 * 举例: words = Observable["a", "a", "b", "c", "c"] 返回: Single[Map{a=2, b=1,
	 * c=2}]
	 */
	public Single<Map<String, Integer>> wordCount2(Observable<String> words) {
		return words.reduce(new HashMap<String, Integer>(), this::reducerFun);
	}

	private Map<String, Integer> reducerFun(Map<String, Integer> map, String s) {
		Integer integer = map.get(s);
		if (integer == null) integer = 0;
		map.put(s, ++integer);
		return map;
	}
}