The source code

    /**
     * @class Ext.grid.PivotGrid
     * @extends Ext.grid.GridPanel
     * <p>The PivotGrid component enables rapid summarization of large data sets. It provides a way to reduce a large set of
     * data down into a format where trends and insights become more apparent. A classic example is in sales data; a company
     * will often have a record of all sales it makes for a given period - this will often encompass thousands of rows of
     * data. The PivotGrid allows you to see how well each salesperson performed, which cities generate the most revenue,
     * how products perform between cities and so on.</p>
     * <p>A PivotGrid is composed of two axes (left and top), one {@link #measure} and one {@link #aggregator aggregation}
     * function. Each axis can contain one or more {@link #dimension}, which are ordered into a hierarchy. Dimensions on the
     * left axis can also specify a width. Each dimension in each axis can specify its sort ordering, defaulting to "ASC",
     * and must specify one of the fields in the {@link Ext.data.Record Record} used by the PivotGrid's
     * {@link Ext.data.Store Store}.</p>
    <pre><code>
    // This is the record representing a single sale
    var SaleRecord = Ext.data.Record.create([
        {name: 'person',   type: 'string'},
        {name: 'product',  type: 'string'},
        {name: 'city',     type: 'string'},
        {name: 'state',    type: 'string'},
        {name: 'year',     type: 'int'},
        {name: 'value',    type: 'int'}
    ]);

    // A simple store that loads SaleRecord data from a url
    var myStore = new Ext.data.Store({
        url: 'data.json',
        autoLoad: true,
        reader: new Ext.data.JsonReader({
            root: 'rows',
            idProperty: 'id'
        }, SaleRecord)
    });

    // Create the PivotGrid itself, referencing the store
    var pivot = new Ext.grid.PivotGrid({
        store     : myStore,
        aggregator: 'sum',
        measure   : 'value',

        leftAxis: [
            {
                width: 60,
                dataIndex: 'product'
            },
            {
                width: 120,
                dataIndex: 'person',
                direction: 'DESC'
            }
        ],

        topAxis: [
            {
                dataIndex: 'year'
            }
        ]
    });
    </code></pre>
     * <p>The specified {@link #measure} is the field from SaleRecord that is extracted from each combination
     * of product and person (on the left axis) and year on the top axis. There may be several SaleRecords in the
     * data set that share this combination, so an array of measure fields is produced. This array is then
     * aggregated using the {@link #aggregator} function.</p>
     * <p>The default aggregator function is sum, which simply adds up all of the extracted measure values. Other
     * built-in aggregator functions are count, avg, min and max. In addition, you can specify your own function.
     * In this example we show the code used to sum the measures, but you can return any value you like. See
     * {@link #aggregator} for more details.</p>
    <pre><code>
    new Ext.grid.PivotGrid({
        aggregator: function(records, measure) {
            var length = records.length,
                total  = 0,
                i;

            for (i = 0; i < length; i++) {
                total += records[i].get(measure);
            }

            return total;
        },

        renderer: function(value) {
            return Math.round(value);
        },

        //your normal config here
    });
    </code></pre>
     * <p><u>Renderers</u></p>
     * <p>PivotGrid optionally accepts a {@link #renderer} function which can modify the data in each cell before it
     * is rendered. The renderer is passed the value that would usually be placed in the cell and is expected to return
     * the new value. For example let's imagine we had height data expressed as a decimal - here's how we might use a
     * renderer to display the data in feet and inches notation:</p>
    <pre><code>
    new Ext.grid.PivotGrid({
        //in each case the value is a decimal number of feet
        renderer  : function(value) {
            var feet   = Math.floor(value),
                inches = Math.round((value - feet) * 12);

            return String.format("{0}' {1}\"", feet, inches);
        },
        //normal config here
    });
    </code></pre>
     * <p><u>Reconfiguring</u></p>
     * <p>All aspects PivotGrid's configuration can be updated at runtime. It is easy to change the {@link #setMeasure measure},
     * {@link #setAggregator aggregation function}, {@link #setLeftAxis left} and {@link #setTopAxis top} axes and refresh the grid.</p>
     * <p>In this case we reconfigure the PivotGrid to have city and year as the top axis dimensions, rendering the average sale
     * value into the cells:</p>
    <pre><code>
    //the left axis can also be changed
    pivot.topAxis.setDimensions([
        {dataIndex: 'city', direction: 'DESC'},
        {dataIndex: 'year', direction: 'ASC'}
    ]);

    pivot.setMeasure('value');
    pivot.setAggregator('avg');

    pivot.view.refresh(true);
    </code></pre>
     * <p>See the {@link Ext.grid.PivotAxis PivotAxis} documentation for further detail on reconfiguring axes.</p>
     */
    Ext.grid.PivotGrid = Ext.extend(Ext.grid.GridPanel, {

        /**
         * @cfg {String|Function} aggregator The aggregation function to use to combine the measures extracted
         * for each dimension combination. Can be any of the built-in aggregators (sum, count, avg, min, max).
         * Can also be a function which accepts two arguments (an array of Records to aggregate, and the measure
         * to aggregate them on) and should return a String.
         */
        aggregator: 'sum',

        /**
         * @cfg {Function} renderer Optional renderer to pass values through before they are rendered to the dom. This
         * gives an opportunity to modify cell contents after the value has been computed.
         */
        renderer: undefined,

        /**
         * @cfg {String} measure The field to extract from each Record when pivoting around the two axes. See the class
         * introduction docs for usage
         */

        /**
         * @cfg {Array|Ext.grid.PivotAxis} leftAxis Either and array of {@link #dimension} to use on the left axis, or
         * a {@link Ext.grid.PivotAxis} instance. If an array is passed, it is turned into a PivotAxis internally.
         */

        /**
         * @cfg {Array|Ext.grid.PivotAxis} topAxis Either and array of {@link #dimension} to use on the top axis, or
         * a {@link Ext.grid.PivotAxis} instance. If an array is passed, it is turned into a PivotAxis internally.
         */

        //inherit docs
        initComponent: function() {
            Ext.grid.PivotGrid.superclass.initComponent.apply(this, arguments);

            this.initAxes();

            //no resizing of columns is allowed yet in PivotGrid
            this.enableColumnResize = false;

            this.viewConfig = Ext.apply(this.viewConfig || {}, {
                forceFit: true
            });

            //TODO: dummy col model that is never used - GridView is too tightly integrated with ColumnModel
            //in 3.x to remove this altogether.
            this.colModel = new Ext.grid.ColumnModel({});
        },

        /**
         * Returns the function currently used to aggregate the records in each Pivot cell
         * @return {Function} The current aggregator function
         */
        getAggregator: function() {
            if (typeof this.aggregator == 'string') {
                return Ext.grid.PivotAggregatorMgr.types[this.aggregator];
            } else {
                return this.aggregator;
            }
        },

        /**
         * Sets the function to use when aggregating data for each cell.
         * @param {String|Function} aggregator The new aggregator function or named function string
         */
        setAggregator: function(aggregator) {
            this.aggregator = aggregator;
        },

        /**
         * Sets the field name to use as the Measure in this Pivot Grid
         * @param {String} measure The field to make the measure
         */
        setMeasure: function(measure) {
            this.measure = measure;
        },

        /**
         * Sets the left axis of this pivot grid. Optionally refreshes the grid afterwards.
         * @param {Ext.grid.PivotAxis} axis The pivot axis
         * @param {Boolean} refresh True to immediately refresh the grid and its axes (defaults to false)
         */
        setLeftAxis: function(axis, refresh) {
            /**
             * The configured {@link Ext.grid.PivotAxis} used as the left Axis for this Pivot Grid
             * @property leftAxis
             * @type Ext.grid.PivotAxis
             */
            this.leftAxis = axis;

            if (refresh) {
                this.view.refresh();
            }
        },

        /**
         * Sets the top axis of this pivot grid. Optionally refreshes the grid afterwards.
         * @param {Ext.grid.PivotAxis} axis The pivot axis
         * @param {Boolean} refresh True to immediately refresh the grid and its axes (defaults to false)
         */
        setTopAxis: function(axis, refresh) {
            /**
             * The configured {@link Ext.grid.PivotAxis} used as the top Axis for this Pivot Grid
             * @property topAxis
             * @type Ext.grid.PivotAxis
             */
            this.topAxis = axis;

            if (refresh) {
                this.view.refresh();
            }
        },

        /**
         * @private
         * Creates the top and left axes. Should usually only need to be called once from initComponent
         */
        initAxes: function() {
            var PivotAxis = Ext.grid.PivotAxis;

            if (!(this.leftAxis instanceof PivotAxis)) {
                this.setLeftAxis(new PivotAxis({
                    orientation: 'vertical',
                    dimensions : this.leftAxis || [],
                    store      : this.store
                }));
            };

            if (!(this.topAxis instanceof PivotAxis)) {
                this.setTopAxis(new PivotAxis({
                    orientation: 'horizontal',
                    dimensions : this.topAxis || [],
                    store      : this.store
                }));
            };
        },

        /**
         * @private
         * @return {Array} 2-dimensional array of cell data
         */
        extractData: function() {
            var records  = this.store.data.items,
                recCount = records.length,
                cells    = [],
                record, i, j, k;

            if (recCount == 0) {
                return [];
            }

            var leftTuples = this.leftAxis.getTuples(),
                leftCount  = leftTuples.length,
                topTuples  = this.topAxis.getTuples(),
                topCount   = topTuples.length,
                aggregator = this.getAggregator();

            for (i = 0; i < recCount; i++) {
                record = records[i];

                for (j = 0; j < leftCount; j++) {
                    cells[j] = cells[j] || [];

                    if (leftTuples[j].matcher(record) === true) {
                        for (k = 0; k < topCount; k++) {
                            cells[j][k] = cells[j][k] || [];

                            if (topTuples[k].matcher(record)) {
                                cells[j][k].push(record);
                            }
                        }
                    }
                }
            }

            var rowCount = cells.length,
                colCount, row;

            for (i = 0; i < rowCount; i++) {
                row = cells[i];
                colCount = row.length;

                for (j = 0; j < colCount; j++) {
                    cells[i][j] = aggregator(cells[i][j], this.measure);
                }
            }

            return cells;
        },

        /**
         * Returns the grid's GridView object.
         * @return {Ext.grid.PivotGridView} The grid view
         */
        getView: function() {
            if (!this.view) {
                this.view = new Ext.grid.PivotGridView(this.viewConfig);
            }

            return this.view;
        }
    });

    Ext.reg('pivotgrid', Ext.grid.PivotGrid);

    Ext.grid.PivotAggregatorMgr = new Ext.AbstractManager();

    Ext.grid.PivotAggregatorMgr.registerType('sum', function(records, measure) {
        var length = records.length,
            total  = 0,
            i;

        for (i = 0; i < length; i++) {
            total += records[i].get(measure);
        }

        return total;
    });

    Ext.grid.PivotAggregatorMgr.registerType('avg', function(records, measure) {
        var length = records.length,
            total  = 0,
            i;

        for (i = 0; i < length; i++) {
            total += records[i].get(measure);
        }

        return (total / length) || 'n/a';
    });

    Ext.grid.PivotAggregatorMgr.registerType('min', function(records, measure) {
        var data   = [],
            length = records.length,
            i;

        for (i = 0; i < length; i++) {
            data.push(records[i].get(measure));
        }

        return Math.min.apply(this, data) || 'n/a';
    });

    Ext.grid.PivotAggregatorMgr.registerType('max', function(records, measure) {
        var data   = [],
            length = records.length,
            i;

        for (i = 0; i < length; i++) {
            data.push(records[i].get(measure));
        }

        return Math.max.apply(this, data) || 'n/a';
    });

    Ext.grid.PivotAggregatorMgr.registerType('count', function(records, measure) {
        return records.length;
    });