如何使用rxjs对数组中的两个字段进行分组？

import { from } from 'rxjs';
import { groupBy, mergeMap, toArray } from 'rxjs/operators';

const data = [
  { id: 1, category: 'A', value: 10 },
  { id: 2, category: 'B', value: 20 },
  { id: 3, category: 'A', value: 30 },
  { id: 4, category: 'B', value: 40 },
  { id: 5, category: 'A', value: 50 },
];

from(data)
  .pipe(
    groupBy(item => item.category),
    mergeMap(group => group.pipe(toArray()))
  )
  .subscribe(result => {
    console.log(result);
  });

[
  { id: 1, category: 'A', value: 10 },
  { id: 3, category: 'A', value: 30 },
  { id: 5, category: 'A', value: 50 }
]
[
  { id: 2, category: 'B', value: 20 },
  { id: 4, category: 'B', value: 40 }
]