RxJava学习(6) : 聚合-Aggregation

前言

根据Froussios英文版的学习笔记。

一、count

计算原始Observable发射物的数量，然后只发射这个值
例如 发射1 2 3 ，count()结果为3

二、first(T defaultItem) 与 firstElement()

1. first :如果没有第一个值，则返回defaultItem
2. firstElement: 如果没有第一个值，则complete 流。

三、last(T defaultItem) 与 lastElement()

同first，只是发射的是最后一个值

四、single(T defaultItem) 与 singleElement()

1. singleElement(): Observable至发射一个数据，否则报错
2. single(T defaultItem) ： 没有发射任何数据，则返回defaultItem

五、reduce、scan与collect

1. reduce :按顺序对Observable发射的每项数据应用一个函数并发射最终的值

   
   reduce

     Observable.just(1,2,4)
            .reduce(new BiFunction<Integer, Integer, Integer>() {
                @Override
                public Integer apply(Integer integer, Integer integer2) throws Exception {
                    Log.d("pngpng",integer+"--"+integer2);
                    return integer+integer2;
                }
            })
            .subscribe(new Consumer<Object>() {
                @Override
                public void accept(Object o) throws Exception {
                    Log.d("pngpng", o + "");
                }
            }, throwable -> Log.e("pngpng", "just error", throwable));

结果如下：

 D/pngpng: 1--2
 D/pngpng: 3--4
 D/pngpng: 7

      Observable.just(1,2,4)
            .reduce(10,new BiFunction<Integer, Integer, Integer>() {
                @Override
                public Integer apply(Integer integer, Integer integer2) throws Exception {
                    Log.d("pngpng",integer+"--"+integer2);
                    return integer+integer2;
                }
            })
            .subscribe(new Consumer<Object>() {
                @Override
                public void accept(Object o) throws Exception {
                    Log.d("pngpng", o + "");
                }
            }, throwable -> Log.e("pngpng", "just error", throwable));

结果如下：

 D/pngpng: 10--1
 D/pngpng: 11--2
 D/pngpng: 13--4
 D/pngpng: 17

2. scan: 连续地对数据序列的每一项应用一个函数，然后连续发射结果

   
   scan

3. collect:收集所有的数据到一个可变的数据结构

     Observable.just(1, 2, 4)
            .collect((Callable<List<Integer>>) ArrayList::new,
                (o, integer) -> {
                    o.add(integer);
                })
            .subscribe(new Consumer<Object>() {
                @Override
                public void accept(Object o) throws Exception {
                    Log.d("pngpng", o + "");
                }
            }, throwable -> Log.e("pngpng", "just error", throwable));

结果为：

 D/pngpng: [1, 2, 4]

六、toList与toSortedList

1. toList :按照顺序获得一个list
2. toSortedList:按照自定义顺序获取list

     Observable.just(1, 2, 4)
            .toSortedList(new Comparator<Integer>() {
                @Override
                public int compare(Integer integer, Integer t1) {
                    return t1-integer;
                }
            })
            .subscribe(new Consumer<Object>() {
                @Override
                public void accept(Object o) throws Exception {
                    Log.d("pngpng", o + "");
                }
            }, throwable -> Log.e("pngpng", "just error", throwable));

结果为：

 D/pngpng: [4, 2, 1]

七、toMap 与toMultimap

1. toMap ：转化成map

public final <K> Observable<java.util.Map<K,T>> toMap(
    Func1<? super T,? extends K> keySelector)
public final <K,V> Observable<java.util.Map<K,V>> toMap(
    Func1<? super T,? extends K> keySelector,
    Func1<? super T,? extends V> valueSelector)
public final <K,V> Observable<java.util.Map<K,V>> toMap(
    Func1<? super T,? extends K> keySelector,
    Func1<? super T,? extends V> valueSelector,
    Func0<? extends java.util.Map<K,V>> mapFactory)

举个例子：

    Observable.just(1, 2, 2, 3)
            .toMap(new Function<Integer, Integer>() {
                @Override
                public Integer apply(Integer integer) throws Exception {
                    return integer;
                }
            }, new Function<Integer, String>() {
                @Override
                public String apply(Integer integer) throws Exception {
                    return integer + "自定义";
                }
            })
            .subscribe(new Consumer<Map<Integer, String>>() {
                @Override
                public void accept(Map<Integer, String> o) throws Exception {
                    Log.d("pngpng", o + "");
                }
            }, throwable -> Log.e("pngpng", "just error", throwable));

结果为：

D/pngpng:  {1=1自定义, 3=3自定义, 2=2自定义}

2. toMutitleMap

    Observable.just(1, 2, 2,3)
            .toMultimap(new Function<Integer, Integer>() {
                @Override
                public Integer apply(Integer integer) throws Exception {
                    return integer ;
                }
            }, new Function<Integer, String>() {
                @Override
                public String apply(Integer integer) throws Exception {
                    return integer+"自定义";
                }
            })
            .subscribe(new Consumer<Map<Integer,Collection<String>>>() {
                @Override
                public void accept(Map<Integer,Collection<String>> o) throws Exception {
                    Log.d("pngpng", o + "");
                }
            }, throwable -> Log.e("pngpng", "just error", throwable));

结果为

 D/pngpng: {1=[1自定义], 3=[3自定义], 2=[2自定义, 2自定义]}