Question

将angular4与rxjs 5.4.0

一起使用

我正在尝试按“类型”对列表进行分组并获取其计数。有人可以帮忙吗？以下是我的代码

export class Sample{
  type:string;
  data:any ...
  ...
}

我有一个Sample Class

数组

list:Sample[] = // number of elements

Observable.from(this.list).groupBy(x=> x.type)
  .flatMap( group => {
    return group.reduce; // how can i use reduce function to count numbers and return map of type and their count
  }
})

Answer 1

你很接近，我认为你只需要在分组的可观察数据上再多运算一次。

const list = [{ type: 'foo' }, { type: 'bar' }, { type: 'bar' }];

Observable.from( list ).groupBy( x => x.type )
  .mergeMap( list$ => { // each emission is a stream

    /* A stream of "aggregated" data. */
    const count$ = list$.count();

    /* Format the result. */
    return count$.map( count => ({ type: list$.key, count }));
  });

这会发出：

{ type: 'foo', total: 1 }
{ type: 'bar', total: 2 }

听起来你可能有更复杂的用例来计算“聚合”，也许你需要总结Sample.data。如果是这样，您只需要使用自己的count$实现更改。假设data是一个数字列表：

const list = [{
  type: 'foo',
  data: [1,2,3]
}, {
  type: 'bar',
  data: [4,5,6]
}, {
  type: 'bar',
  data: [7,8,9]
}];

Observable.from( list ).groupBy( x => x.type )
  .mergeMap( list$ => { // each emission is a stream

    /* A stream of "aggregated" data. */
    const count$ = list$.reduce( ( accumulator, sample ) => { // reduce the stream
      return accumulator + sample.data.reduce( ( acc, datum ) => { // reduce the array
        return acc + datum;
      }, 0);
    }, 0);

    /* Format the result. */
    return count$.map( count => ({ type: list$.key, count }));
  });

这会产生：

{ type: 'foo', total: 6 }
{ type: 'bar', total: 39 }

angular2 rxjs groupby with count

1 个答案: