sum/count

I have this data:

data: any[] = [
  {
    "projMgr": "Tom",
    "projNam": "111.2 Planning",
    "baseCost": 10000,
    "designCost": 1000,
  },
  {
    "projMgr": "Tom",
    "projNam": "111.2 Planning",
    "baseCost": 10000,
    "designCost": 2000,
  },
  {
    "projMgr": "Tom",
    "projNam": "111.3 Assembly",
    "baseCost": 20000,
    "designCost": 2000,
  },
  {
    "projMgr": "Mary",
    "projNam": "111.6 Test",
    "baseCost": 20000,
    "designCost": 100,
  }
];

And this configuration:

 
  p_rows = [
    {caption: 'Project Manager', uniqueName: 'projMgr'},
    {caption: 'Project Name', uniqueName: 'projNam'}
  ];
  p_measures = [
    {caption: 'Design Cost', uniqueName: '[designCost]', aggregation: 'sum', format: 'currency', active: true}
  ];

I tried doing average:

{
  caption: 'Base Cost',
  uniqueName: '[baseCost]',
  aggregation: 'average',
  format: 'currency',
  active: true
}

which works at the project level because it averages out. However, Tom's Total should be $30,000 instead of another average $13,333.

I almost need sum("baseCost")/count("baseCost") but that doesn't seem to work.