Weighted Average (Final Solution - Hopefully!)

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/**
 * This is the final solution for the weighted average calculation.  This example 
 * includes grouping of by two columns (country and type) and then calculating
 * the weighted average for interest.
 * 
 * @author Ben Northrop
 */
var columnDefs = [{
  headerName: "Country",
  field: "country",
  rowGroup: true,
  hide: true
}, {
  headerName: "Type",
  field: "type",
  rowGroup: true,
  hide: true
}, {
  headerName: "Book Value",
  field: "bookValue"
}, {
  headerName: "Interest",
  field: "interest"
}];

var gridOptions = {
  columnDefs: columnDefs,
  animateRows: true,
  enableRangeSelection: true,
  rowData: createRowData(),
  enableSorting: true,
  enableFilter: true,
  suppressAggFuncInHeader: true,
  groupUseEntireRow: false, // need this?
  groupRowAggNodes: groupRowAggNodes,
};


/**
 * Built-in callback function that's executed on each group roll-up.  We use this to calculate the 
 * weighted average for interest which equals SUM(bookValue * interest)/ SUM(bookValue).
 * 
 * @see https://www.ag-grid.com/javascript-grid-aggregation/#gsc.tab=0
 * @see https://plnkr.co/edit/?p=preview
 */
function groupRowAggNodes(nodes) {

  let result = {
    bookValue: 0,
    interest: 0
  };

  let sumBookValue = 0;
  let sumProductInterest = 0;
  nodes.forEach(node => {
    var data = node.group ? node.aggData : node.data;
    sumBookValue += data.bookValue;
    sumProductInterest += (data.bookValue * data.interest);
  });

  result.bookValue = sumBookValue;
  result.interest = sumProductInterest / sumBookValue;

  return result;
}

function createRowData() {
  var rowData = [{
    country: 'US',
    type: 'Bond',
    bookValue: 24,
    interest: 2.4
  }, {
    country: 'US',
    type: 'Bond',
    bookValue: 35,
    interest: 3.1
  }, {
    country: 'US',
    type: 'Loan',
    bookValue: 65,
    interest: 2.5
  }, {
    country: 'US',
    type: 'Loan',
    bookValue: 72,
    interest: 1.8
  }, {
    country: 'UK',
    type: 'Bond',
    bookValue: 68,
    interest: 3.6
  }, {
    country: 'UK',
    type: 'Bond',
    bookValue: 79,
    interest: 4.2
  }, {
    country: 'UK',
    type: 'Loan',
    bookValue: 124,
    interest: 2.8
  }, {
    country: 'UK',
    type: 'Loan',
    bookValue: 98,
    interest: 2.6
  }];

  return rowData;
}


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