How to use the aurelia-slickgrid.Aggregators.Sum function in aurelia-slickgrid

groupByDurationEffortDriven() {
    this.dataviewObj.setGrouping([
      {
        getter: 'duration',
        formatter: (g) => {
          return `Duration:  ${g.value}  <span style="color:green">(${g.count} items)</span>`;
        },
        aggregators: [
          new Aggregators.Sum('duration'),
          new Aggregators.Sum('cost')
        ],
        aggregateCollapsed: true,
        lazyTotalsCalculation: true
      },
      {
        getter: 'effortDriven',
        formatter: (g) =&gt; {
          return `Effort-Driven:  ${(g.value ? 'True' : 'False')} <span style="color:green">(${g.count} items)</span>`;
        },
        aggregators: [
          new Aggregators.Avg('percentComplete'),
          new Aggregators.Sum('cost')
        ],
        collapsed: true,
        lazyTotalsCalculation: true

},
        aggregators: [
          new Aggregators.Sum('duration'),
          new Aggregators.Sum('cost')
        ],
        aggregateCollapsed: true,
        lazyTotalsCalculation: true
      },
      {
        getter: 'effortDriven',
        formatter: (g) => {
          return `Effort-Driven:  ${(g.value ? 'True' : 'False')} <span style="color:green">(${g.count} items)</span>`;
        },
        aggregators: [
          new Aggregators.Avg('percentComplete'),
          new Aggregators.Sum('cost')
        ],
        collapsed: true,
        lazyTotalsCalculation: true
      }
    ]);
  }

groupByDuration() {
    this.dataviewObj.setGrouping({
      getter: 'duration',
      formatter: (g) => {
        return `Duration:  ${g.value} <span style="color:green">(${g.count} items)</span>`;
      },
      comparer: (a, b) =&gt; {
        return Sorters.numeric(a.value, b.value, SortDirectionNumber.asc);
      },
      aggregators: [
        new Aggregators.Avg('percentComplete'),
        new Aggregators.Sum('cost')
      ],
      aggregateCollapsed: false,
      lazyTotalsCalculation: true
    });
  }

},
        aggregators: [
          new Aggregators.Sum('duration'),
          new Aggregators.Sum('cost')
        ],
        aggregateCollapsed: true,
        lazyTotalsCalculation: true
      },
      {
        getter: 'effortDriven',
        formatter: (g) => {
          return `Effort-Driven:  ${(g.value ? 'True' : 'False')} <span style="color:green">(${g.count} items)</span>`;
        },
        aggregators: [
          new Aggregators.Avg('percentComplete'),
          new Aggregators.Sum('cost')
        ],
        collapsed: true,
        lazyTotalsCalculation: true
      }
    ]);
  }

return `Duration:  ${g.value}  <span style="color:green">(${g.count} items)</span>`;
        },
        aggregators: [
          new Aggregators.Sum('duration'),
          new Aggregators.Sum('cost')
        ],
        aggregateCollapsed: true,
        lazyTotalsCalculation: true
      },
      {
        getter: 'effortDriven',
        formatter: (g) =&gt; {
          return `Effort-Driven:  ${(g.value ? 'True' : 'False')}  <span style="color:green">(${g.count} items)</span>`;
        },
        aggregators: [
          new Aggregators.Sum('duration'),
          new Aggregators.Sum('cost')
        ],
        lazyTotalsCalculation: true
      },
      {
        getter: 'percentComplete',
        formatter: (g) =&gt; {
          return `% Complete:  ${g.value}  <span style="color:green">(${g.count} items)</span>`;
        },
        aggregators: [
          new Aggregators.Avg('percentComplete')
        ],
        aggregateCollapsed: true,
        collapsed: true,
        lazyTotalsCalculation: true
      }

groupByDurationOrderByCount(aggregateCollapsed) {
    this.dataviewObj.setGrouping({
      getter: 'duration',
      formatter: (g) => {
        return `Duration:  ${g.value} <span style="color:green">(${g.count} items)</span>`;
      },
      comparer: (a, b) =&gt; {
        return a.count - b.count;
      },
      aggregators: [
        new Aggregators.Avg('percentComplete'),
        new Aggregators.Sum('cost')
      ],
      aggregateCollapsed,
      lazyTotalsCalculation: true
    });
  }

groupByDurationEffortDriven() {
    this.dataviewObj.setGrouping([
      {
        getter: 'duration',
        formatter: (g) => {
          return `Duration:  ${g.value}  <span style="color:green">(${g.count} items)</span>`;
        },
        aggregators: [
          new Aggregators.Sum('duration'),
          new Aggregators.Sum('cost')
        ],
        aggregateCollapsed: true,
        lazyTotalsCalculation: true
      },
      {
        getter: 'effortDriven',
        formatter: (g) =&gt; {
          return `Effort-Driven:  ${(g.value ? 'True' : 'False')} <span style="color:green">(${g.count} items)</span>`;
        },
        aggregators: [
          new Aggregators.Avg('percentComplete'),
          new Aggregators.Sum('cost')
        ],
        collapsed: true,
        lazyTotalsCalculation: true

},
        aggregators: [
          new Aggregators.Sum('duration'),
          new Aggregators.Sum('cost')
        ],
        aggregateCollapsed: true,
        lazyTotalsCalculation: true
      },
      {
        getter: 'effortDriven',
        formatter: (g) => {
          return `Effort-Driven:  ${(g.value ? 'True' : 'False')}  <span style="color:green">(${g.count} items)</span>`;
        },
        aggregators: [
          new Aggregators.Sum('duration'),
          new Aggregators.Sum('cost')
        ],
        lazyTotalsCalculation: true
      },
      {
        getter: 'percentComplete',
        formatter: (g) =&gt; {
          return `% Complete:  ${g.value}  <span style="color:green">(${g.count} items)</span>`;
        },
        aggregators: [
          new Aggregators.Avg('percentComplete')
        ],
        aggregateCollapsed: true,
        collapsed: true,
        lazyTotalsCalculation: true
      }
    ]);

groupByDurationEffortDrivenPercent() {
    this.dataviewObj.setGrouping([
      {
        getter: 'duration',
        formatter: (g) => {
          return `Duration:  ${g.value}  <span style="color:green">(${g.count} items)</span>`;
        },
        aggregators: [
          new Aggregators.Sum('duration'),
          new Aggregators.Sum('cost')
        ],
        aggregateCollapsed: true,
        lazyTotalsCalculation: true
      },
      {
        getter: 'effortDriven',
        formatter: (g) =&gt; {
          return `Effort-Driven:  ${(g.value ? 'True' : 'False')}  <span style="color:green">(${g.count} items)</span>`;
        },
        aggregators: [
          new Aggregators.Sum('duration'),
          new Aggregators.Sum('cost')
        ],
        lazyTotalsCalculation: true
      },
      {

groupByDurationEffortDrivenPercent() {
    this.dataviewObj.setGrouping([
      {
        getter: 'duration',
        formatter: (g) => {
          return `Duration:  ${g.value}  <span style="color:green">(${g.count} items)</span>`;
        },
        aggregators: [
          new Aggregators.Sum('duration'),
          new Aggregators.Sum('cost')
        ],
        aggregateCollapsed: true,
        lazyTotalsCalculation: true
      },
      {
        getter: 'effortDriven',
        formatter: (g) =&gt; {
          return `Effort-Driven:  ${(g.value ? 'True' : 'False')}  <span style="color:green">(${g.count} items)</span>`;
        },
        aggregators: [
          new Aggregators.Sum('duration'),
          new Aggregators.Sum('cost')
        ],
        lazyTotalsCalculation: true
      },