RxJava操作符之 scan与reduce的区别

迈不过友情╰ 2023-07-07 12:44 14阅读 0赞

RxJava中的scan和reduce的作用比较相近，都是把前一次的计算结果作为参数传入下一次计算中。它们的官方定义分别如下：

> **scan：**  
> apply a function to each item emitted by an Observable, sequentially,  
> and emit each successive value

> **reduce：**  
> apply a function to each item emitted by an Observable, sequentially,  
> and emit the final value

从定义我们一目了然它们的区别在于下半句：

*  scan会将每次计算的结构都发送到下游；
 *  而reduce只会将最终结果发送到下游，complete为止不会收到第二次数据

# scan #

--------------------

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3ZpdGF2aXZh_size_16_color_FFFFFF_t_70]

Observable.range(1, 5)
                .scan {  result: Int, result2: Int ->
                    println("result $result result2 $result2")
                    result + result2
                }
                .subscribe { 
                    println("integer $it")
                }

output：
    ----------
    result 1
    x 1 y 2
    result 3
    x 3 y 3
    result 6
    x 6 y 4
    result 10
    x 10 y 5
    result 15

# reduce #

--------------------

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3ZpdGF2aXZh_size_16_color_FFFFFF_t_70 1]

Observable.range(1, 5)
            .reduce {  x: Int, y: Int ->
                println("x $x y $y")
                x + y
            }
            .subscribe { 
                println("result $it")
            }

output:
    -----------
    x 1 y 2
    x 3 y 3
    x 6 y 4
    x 10 y 5
    result 15

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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3ZpdGF2aXZh_size_16_color_FFFFFF_t_70 1]: https://img-blog.csdnimg.cn/20200223180711444.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3ZpdGF2aXZh,size_16,color_FFFFFF,t_70