如何使用RxJs distinctUntilChanged？ [英] How to use RxJs distinctUntilChanged?

问题描述

我开始使用RxJs（使用v5测试版），但不知何故我无法弄清楚如何使用 distinctUntilChanged 。如果我在babel-node中运行它，下面代码的输出是

I'm getting started with RxJs (using the v5 beta), but somehow I can't figure out how to work with distinctUntilChanged. The output from the code below if I run it in babel-node is

[ 'a', 1 ]
{ key: 'a', state: 1 }
Next:  { value: 42 }
Completed

这不是我所期望的。为什么只有一个条目通过 distinctUntilChanged ？我希望输出为

That is not what I would expect. Why is only one entry passing distinctUntilChanged? I would expect the output to be

[ 'a', 1 ]
[ 'a', 0 ]
[ 'a', 1 ]
{ key: 'a', state: 1 }
{ key: 'a', state: 2 }
{ key: 'a', state: 0 }
{ key: 'a', state: 1 }
Next:  { value: 42 }
Next:  { value: 24 }
Completed

这是代码

import {Observable} from 'rxjs'

Observable.of(['a', 1], ['a', 1], ['a', 0], ['a', 1])
  .distinctUntilChanged(x => x[1])
  .subscribe(x => console.log(x))

Observable.of({key: 'a', state: 1}, {key: 'a', state: 2}, {key: 'a', state: 0}, {key: 'a', state: 1})
  .distinctUntilChanged(x => x.state)
  .subscribe(x => console.log(x))

Observable.of({value: 42}, {value: 42}, {value: 24}, {value: 24})
  .distinctUntilChanged(x => x.value)
  .subscribe(
    function (x) {
      console.log('Next: ', x)
    },
    function (err) {
      console.log('Error: ' + err)
    },
    function () {
      console.log('Completed')
    }
  )

这些功能的v5文档中的链接似乎是死了

The links in the v5 docs for these functions appear to be dead

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一些额外的调试：

Observable.of(['a', 1], ['a', 1], ['a', 0], ['a', 1])
  .do(x => console.log('before', x))
  .distinctUntilChanged(x => x[1])
  .do(x => console.log('after', x))
  .subscribe(x => console.log(x))

输出：

before [ 'a', 1 ]
after [ 'a', 1 ]
[ 'a', 1 ]
before [ 'a', 1 ]
before [ 'a', 0 ]
before [ 'a', 1 ]

推荐答案

我得到了答案此处。基本上函数签名从（键选择器，比较器）变为（比较器，键选择器）。

I got an answer here. Basically the function signature changed from (key selector, comparator) to (comparator, key selector).

这是在v5中完成示例的方式：

This is how the example is done in v5:

Observable.of(['a', 1], ['a', 1], ['a', 0], ['a', 1])
  .distinctUntilChanged(null, x => x[1])
  .subscribe(x => console.log(x))

这篇关于如何使用RxJs distinctUntilChanged？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！