Dynamically change grind size in Angular 6

Question

In my application, I have to delete few row from ag-grid based on user input , I am using something like below

  rowsToDelete:RowDataTransaction = {remove: userSelectedRows};
  this.gridOptions.api.updateDataRow(rowsToDelete); 

After execution of above code grid removes rows part of Array "userSelectedRows", However if i try to get the size of grid using

  let size =this.gridOptions.rowData.lenght, 

Still i am getting actual size.

So how can i get update grid size after rows are deleted?

Apologies i couldn't paste actual code here due to my firm policy.