哪个rxjs运算符在映射后进行额外的转换? [英] Which rxjs operator to make extra transformation after mapping?

问题描述

 this.service.retrieveObject(id).map((object)=>{ return transformation1(object); })
                                .map((object)=>{ return transformation2(object); });

在示例中，在 transformation1 被释放后，第二个 map 调用无法访问对象.

In the exemple bellow the second map call doesn't have access to object after transformation1 exexuted.

我需要使用哪个运算符进行嵌套转换(transformation2优于transformation1)?

Which operator do I need to use to make nested transformations (transformation2 over transformation1)?

推荐答案

map 是进行转换的正确运算符. map 本质上是 a->b 函数，您可以在其中输入 a 并输出 b .随后对 map 的调用将获取输出对象.

map is the correct operator to make transformations. map is essentially an a -> b function where you input an a and output a b. Any subsequent calls to map would get the output object.

两次调用 map 的缺点是，您实际上在对象上进行了两次迭代.虽然在小对象上虽然没什么大不了，但是列表很大，性能会下降.您可以将 transformation1 和 transformation2 函数有效地组合为一个函数，并且仅调用一次 map .或者让 transformation2 从 transformation1 获取返回对象.将这两种操作合并到一个调用中会更有效.

The downside the calling map twice is that you are effectively iterating over the object twice. While on small objects that might not be a big deal, but take a large list and performance will decrease. You can effectively combine your transformation1 and transformation2 functions into a single function and only call map once. Or make transformation2 take the return object from transformation1. It would be more efficient to combine both operations into a single call.

this.service.retrieveObject(id)
    .map(object => transformation2(transformation1(object)));

更新1/17/2018

如果Transformation1和Transformation2是异步的，那么使用 switchMap 怎么办? switchMap 从第一个可观察对象获取结果，并将其传递给第二个可观察对象.

If transformation1 and transformation2 are asynchronous, what about using switchMap? switchMap takes the result from the first observable and passes it to the second observable.

this.service.retrieveObject(id)
    .switchMap(retrieveObjectResponse => transformation1(retrieveObjectResponse))
    .switchMap(transformation1Response => transformation2(transformation1Response)); 

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