# Custom Aggregates in FlexGrid

Learn how to create custom aggregates using FlexGrid in this documentation topic

## Content

The FlexGrid columns have an **aggregate** property that allows you to show data summaries for the whole grid or for each group.

In some cases, however, the **aggregate** property is not flexible enough, and you may need to calculate aggregates using custom code.

The grid below includes a 'Profit' column that shows the difference between 'Sales' and 'Expenses'.

The 'Profit' column is calculated in the **formatItem** event. The profit for regular data items is based on the actual data items. The profit for groups is calculated using the group's **getAggregate** method.
```javascript
import * as wjCore from '@mescius/wijmo';
import * as wjGrid from '@mescius/wijmo.grid';

// create a group to show the grand totals
var grandTotalsGroup = new wjCore.PropertyGroupDescription('Grand Total', 
    function(item, propName) {
        return '';
    }
);

// grid with custom aggregates
var theGrid = new wjGrid.FlexGrid('#theGrid', {
    autoGenerateColumns: false,
        columns: [ // column definitions with aggregates
        { binding: 'id', header: 'ID', width: 60, isReadOnly: true },
        { binding: 'country', header: 'Country' },
        { binding: 'product', header: 'Product' },
        { binding: 'sales', header: 'Sales', aggregate: 'Sum' },
        { binding: 'expenses', header: 'Expenses', aggregate: 'Sum' },
        { binding: 'profit', header: 'Profit', dataType: 'Number', isReadOnly: true }
    ],
    itemsSource: new wjCore.CollectionView(data, {
        groupDescriptions: [
        grandTotalsGroup,
        'country'
        ]
    })
});

// custom cell calculation
theGrid.formatItem.addHandler(function(s, e) {

// cells and column footer panels only
if (e.panel == s.cells) {
    // get row, column, and data item (or group description)
    var r = s.rows[e.row];
    var c = s.columns[e.col];
    var item = s.rows[e.row].dataItem;
    var group = r instanceof wjGrid.GroupRow ? item : null;

    // assume value is not negative
    var negative = false;

    // calculate profit
    if (c.binding == 'profit') {
        var profit = group
            ? group.getAggregate('Sum', 'sales') - group.getAggregate('Sum', 'expenses')
            : item.sales - item.expenses;
        e.cell.textContent = wjCore.Globalize.format(profit, c.format);
        negative = profit < 0;
    }
    // update 'negative' class on cell
    wijmo.toggleClass(e.cell, 'negative', negative);
    }
});
```