igniteui-angular/lib/data-operations/grouping-expression.interface.d.ts

Ignite UI for Angular is a dependency-free Angular toolkit for building modern web apps

import { ISortingExpression } from './sorting-strategy';
export interface IGroupingExpression extends ISortingExpression {
    groupingComparer?: (a: any, b: any, currRec?: any, groupRec?: any) => number;
}