您可以在将数据设置为dataSource之前对其进行更改. 例如，如果您可以观察到一些http数据，则可以执行以下操作:

You could make changes in data before setting it to dataSource. For example, if you get some http data as observable, you could do:

this.data$ = this.certificateService.certificates$.pipe(
        map(data => {
          data.column5 = data.column4 // and make all other calculations
          return data;
       })
);

然后您可以订阅数据并将其设置在数据源中

Then you could subscribe on data and set it in datasource

 this.data$.subscribe(data => {
   this.dataSource = new MatTableDataSource(data)
 })