The source code

    /**
     * @class Ext.grid.GroupingView
     * @extends Ext.grid.GridView
     * Adds the ability for single level grouping to the grid. A {@link Ext.data.GroupingStore GroupingStore}
     * must be used to enable grouping.  Some grouping characteristics may also be configured at the
     * {@link Ext.grid.Column Column level}<div class="mdetail-params"><ul>
     * <li><code>{@link Ext.grid.Column#emptyGroupText emptyGroupText}</code></li>
     * <li><code>{@link Ext.grid.Column#groupable groupable}</code></li>
     * <li><code>{@link Ext.grid.Column#groupName groupName}</code></li>
     * <li><code>{@link Ext.grid.Column#groupRender groupRender}</code></li>
     * </ul></div>
     * <p>Sample usage:</p>
     * <pre><code>
    var grid = new Ext.grid.GridPanel({
        // A groupingStore is required for a GroupingView
        store: new {@link Ext.data.GroupingStore}({
            autoDestroy: true,
            reader: reader,
            data: xg.dummyData,
            sortInfo: {field: 'company', direction: 'ASC'},
            {@link Ext.data.GroupingStore#groupOnSort groupOnSort}: true,
            {@link Ext.data.GroupingStore#remoteGroup remoteGroup}: true,
            {@link Ext.data.GroupingStore#groupField groupField}: 'industry'
        }),
        colModel: new {@link Ext.grid.ColumnModel}({
            columns:[
                {id:'company',header: 'Company', width: 60, dataIndex: 'company'},
                // {@link Ext.grid.Column#groupable groupable}, {@link Ext.grid.Column#groupName groupName}, {@link Ext.grid.Column#groupRender groupRender} are also configurable at column level
                {header: 'Price', renderer: Ext.util.Format.usMoney, dataIndex: 'price', {@link Ext.grid.Column#groupable groupable}: false},
                {header: 'Change', dataIndex: 'change', renderer: Ext.util.Format.usMoney},
                {header: 'Industry', dataIndex: 'industry'},
                {header: 'Last Updated', renderer: Ext.util.Format.dateRenderer('m/d/Y'), dataIndex: 'lastChange'}
            ],
            defaults: {
                sortable: true,
                menuDisabled: false,
                width: 20
            }
        }),

        view: new Ext.grid.GroupingView({
            {@link Ext.grid.GridView#forceFit forceFit}: true,
            // custom grouping text template to display the number of items per group
            {@link #groupTextTpl}: '{text} ({[values.rs.length]} {[values.rs.length > 1 ? "Items" : "Item"]})'
        }),

        frame:true,
        width: 700,
        height: 450,
        collapsible: true,
        animCollapse: false,
        title: 'Grouping Example',
        iconCls: 'icon-grid',
        renderTo: document.body
    });
     * </code></pre>
     * @constructor
     * @param {Object} config
     */
    Ext.grid.GroupingView = Ext.extend(Ext.grid.GridView, {

        /**
         * @cfg {String} groupByText Text displayed in the grid header menu for grouping by a column
         * (defaults to 'Group By This Field').
         */
        groupByText : 'Group By This Field',
        /**
         * @cfg {String} showGroupsText Text displayed in the grid header for enabling/disabling grouping
         * (defaults to 'Show in Groups').
         */
        showGroupsText : 'Show in Groups',
        /**
         * @cfg {Boolean} hideGroupedColumn <tt>true</tt> to hide the column that is currently grouped (defaults to <tt>false</tt>)
         */
        hideGroupedColumn : false,
        /**
         * @cfg {Boolean} showGroupName If <tt>true</tt> will display a prefix plus a ': ' before the group field value
         * in the group header line.  The prefix will consist of the <tt><b>{@link Ext.grid.Column#groupName groupName}</b></tt>
         * (or the configured <tt><b>{@link Ext.grid.Column#header header}</b></tt> if not provided) configured in the
         * {@link Ext.grid.Column} for each set of grouped rows (defaults to <tt>true</tt>).
         */
        showGroupName : true,
        /**
         * @cfg {Boolean} startCollapsed <tt>true</tt> to start all groups collapsed (defaults to <tt>false</tt>)
         */
        startCollapsed : false,
        /**
         * @cfg {Boolean} enableGrouping <tt>false</tt> to disable grouping functionality (defaults to <tt>true</tt>)
         */
        enableGrouping : true,
        /**
         * @cfg {Boolean} enableGroupingMenu <tt>true</tt> to enable the grouping control in the column menu (defaults to <tt>true</tt>)
         */
        enableGroupingMenu : true,
        /**
         * @cfg {Boolean} enableNoGroups <tt>true</tt> to allow the user to turn off grouping (defaults to <tt>true</tt>)
         */
        enableNoGroups : true,
        /**
         * @cfg {String} emptyGroupText The text to display when there is an empty group value (defaults to <tt>'(None)'</tt>).
         * May also be specified per column, see {@link Ext.grid.Column}.{@link Ext.grid.Column#emptyGroupText emptyGroupText}.
         */
        emptyGroupText : '(None)',
        /**
         * @cfg {Boolean} ignoreAdd <tt>true</tt> to skip refreshing the view when new rows are added (defaults to <tt>false</tt>)
         */
        ignoreAdd : false,
        /**
         * @cfg {String} groupTextTpl The template used to render the group header (defaults to <tt>'{text}'</tt>).
         * This is used to format an object which contains the following properties:
         * <div class="mdetail-params"><ul>
         * <li><b>group</b> : String<p class="sub-desc">The <i>rendered</i> value of the group field.
         * By default this is the unchanged value of the group field. If a <tt><b>{@link Ext.grid.Column#groupRenderer groupRenderer}</b></tt>
         * is specified, it is the result of a call to that function.</p></li>
         * <li><b>gvalue</b> : Object<p class="sub-desc">The <i>raw</i> value of the group field.</p></li>
         * <li><b>text</b> : String<p class="sub-desc">The configured header (as described in <tt>{@link #showGroupName})</tt>
         * if <tt>{@link #showGroupName}</tt> is <tt>true</tt>) plus the <i>rendered</i> group field value.</p></li>
         * <li><b>groupId</b> : String<p class="sub-desc">A unique, generated ID which is applied to the
         * View Element which contains the group.</p></li>
         * <li><b>startRow</b> : Number<p class="sub-desc">The row index of the Record which caused group change.</p></li>
         * <li><b>rs</b> : Array<p class="sub-desc">Contains a single element: The Record providing the data
         * for the row which caused group change.</p></li>
         * <li><b>cls</b> : String<p class="sub-desc">The generated class name string to apply to the group header Element.</p></li>
         * <li><b>style</b> : String<p class="sub-desc">The inline style rules to apply to the group header Element.</p></li>
         * </ul></div></p>
         * See {@link Ext.XTemplate} for information on how to format data using a template. Possible usage:<pre><code>
    var grid = new Ext.grid.GridPanel({
        ...
        view: new Ext.grid.GroupingView({
            groupTextTpl: '{text} ({[values.rs.length]} {[values.rs.length > 1 ? "Items" : "Item"]})'
        }),
    });
         * </code></pre>
         */
        groupTextTpl : '{text}',

        /**
         * @cfg {String} groupMode Indicates how to construct the group identifier. <tt>'value'</tt> constructs the id using
         * raw value, <tt>'display'</tt> constructs the id using the rendered value. Defaults to <tt>'value'</tt>.
         */
        groupMode: 'value',

        /**
         * @cfg {Function} groupRenderer This property must be configured in the {@link Ext.grid.Column} for
         * each column.
         */

        /**
         * @cfg {Boolean} cancelEditOnToggle True to cancel any editing when the group header is toggled. Defaults to <tt>true</tt>.
         */
        cancelEditOnToggle: true,

        // private
        initTemplates : function(){
            Ext.grid.GroupingView.superclass.initTemplates.call(this);
            this.state = {};

            var sm = this.grid.getSelectionModel();
            sm.on(sm.selectRow ? 'beforerowselect' : 'beforecellselect',
                    this.onBeforeRowSelect, this);

            if(!this.startGroup){
                this.startGroup = new Ext.XTemplate(
                    '<div id="{groupId}" class="x-grid-group {cls}">',
                        '<div id="{groupId}-hd" class="x-grid-group-hd" style="{style}"><div class="x-grid-group-title">', this.groupTextTpl ,'</div></div>',
                        '<div id="{groupId}-bd" class="x-grid-group-body">'
                );
            }
            this.startGroup.compile();

            if (!this.endGroup) {
                this.endGroup = '</div></div>';
            }
        },

        // private
        findGroup : function(el){
            return Ext.fly(el).up('.x-grid-group', this.mainBody.dom);
        },

        // private
        getGroups : function(){
            return this.hasRows() ? this.mainBody.dom.childNodes : [];
        },

        // private
        onAdd : function(ds, records, index) {
            if (this.canGroup() && !this.ignoreAdd) {
                var ss = this.getScrollState();
                this.fireEvent('beforerowsinserted', ds, index, index + (records.length-1));
                this.refresh();
                this.restoreScroll(ss);
                this.fireEvent('rowsinserted', ds, index, index + (records.length-1));
            } else if (!this.canGroup()) {
                Ext.grid.GroupingView.superclass.onAdd.apply(this, arguments);
            }
        },

        // private
        onRemove : function(ds, record, index, isUpdate){
            Ext.grid.GroupingView.superclass.onRemove.apply(this, arguments);
            var g = document.getElementById(record._groupId);
            if(g && g.childNodes[1].childNodes.length < 1){
                Ext.removeNode(g);
            }
            this.applyEmptyText();
        },

        // private
        refreshRow : function(record){
            if(this.ds.getCount()==1){
                this.refresh();
            }else{
                this.isUpdating = true;
                Ext.grid.GroupingView.superclass.refreshRow.apply(this, arguments);
                this.isUpdating = false;
            }
        },

        // private
        beforeMenuShow : function(){
            var item, items = this.hmenu.items, disabled = this.cm.config[this.hdCtxIndex].groupable === false;
            if((item = items.get('groupBy'))){
                item.setDisabled(disabled);
            }
            if((item = items.get('showGroups'))){
                item.setDisabled(disabled);
                item.setChecked(this.canGroup(), true);
            }
        },

        // private
        renderUI : function(){
            var markup = Ext.grid.GroupingView.superclass.renderUI.call(this);

            if(this.enableGroupingMenu && this.hmenu){
                this.hmenu.add('-',{
                    itemId:'groupBy',
                    text: this.groupByText,
                    handler: this.onGroupByClick,
                    scope: this,
                    iconCls:'x-group-by-icon'
                });
                if(this.enableNoGroups){
                    this.hmenu.add({
                        itemId:'showGroups',
                        text: this.showGroupsText,
                        checked: true,
                        checkHandler: this.onShowGroupsClick,
                        scope: this
                    });
                }
                this.hmenu.on('beforeshow', this.beforeMenuShow, this);
            }
            return markup;
        },

        processEvent: function(name, e){
            Ext.grid.GroupingView.superclass.processEvent.call(this, name, e);
            var hd = e.getTarget('.x-grid-group-hd', this.mainBody);
            if(hd){
                // group value is at the end of the string
                var field = this.getGroupField(),
                    prefix = this.getPrefix(field),
                    groupValue = hd.id.substring(prefix.length),
                    emptyRe = new RegExp('gp-' + Ext.escapeRe(field) + '--hd');

                // remove trailing '-hd'
                groupValue = groupValue.substr(0, groupValue.length - 3);

                // also need to check for empty groups
                if(groupValue || emptyRe.test(hd.id)){
                    this.grid.fireEvent('group' + name, this.grid, field, groupValue, e);
                }
                if(name == 'mousedown' && e.button == 0){
                    this.toggleGroup(hd.parentNode);
                }
            }

        },

        // private
        onGroupByClick : function(){
            var grid = this.grid;
            this.enableGrouping = true;
            grid.store.groupBy(this.cm.getDataIndex(this.hdCtxIndex));
            grid.fireEvent('groupchange', grid, grid.store.getGroupState());
            this.beforeMenuShow(); // Make sure the checkboxes get properly set when changing groups
            this.refresh();
        },

        // private
        onShowGroupsClick : function(mi, checked){
            this.enableGrouping = checked;
            if(checked){
                this.onGroupByClick();
            }else{
                this.grid.store.clearGrouping();
                this.grid.fireEvent('groupchange', this, null);
            }
        },

        /**
         * Toggle the group that contains the specific row.
         * @param {Number} rowIndex The row inside the group
         * @param {Boolean} expanded (optional)
         */
        toggleRowIndex : function(rowIndex, expanded){
            if(!this.canGroup()){
                return;
            }
            var row = this.getRow(rowIndex);
            if(row){
                this.toggleGroup(this.findGroup(row), expanded);
            }
        },

        /**
         * Toggles the specified group if no value is passed, otherwise sets the expanded state of the group to the value passed.
         * @param {String} groupId The groupId assigned to the group (see getGroupId)
         * @param {Boolean} expanded (optional)
         */
        toggleGroup : function(group, expanded){
            var gel = Ext.get(group),
                id = Ext.util.Format.htmlEncode(gel.id);

            expanded = Ext.isDefined(expanded) ? expanded : gel.hasClass('x-grid-group-collapsed');
            if(this.state[id] !== expanded){
                if (this.cancelEditOnToggle !== false) {
                    this.grid.stopEditing(true);
                }
                this.state[id] = expanded;
                gel[expanded ? 'removeClass' : 'addClass']('x-grid-group-collapsed');
            }
        },

        /**
         * Toggles all groups if no value is passed, otherwise sets the expanded state of all groups to the value passed.
         * @param {Boolean} expanded (optional)
         */
        toggleAllGroups : function(expanded){
            var groups = this.getGroups();
            for(var i = 0, len = groups.length; i < len; i++){
                this.toggleGroup(groups[i], expanded);
            }
        },

        /**
         * Expands all grouped rows.
         */
        expandAllGroups : function(){
            this.toggleAllGroups(true);
        },

        /**
         * Collapses all grouped rows.
         */
        collapseAllGroups : function(){
            this.toggleAllGroups(false);
        },

        // private
        getGroup : function(v, r, groupRenderer, rowIndex, colIndex, ds){
            var column = this.cm.config[colIndex],
                g = groupRenderer ? groupRenderer.call(column.scope, v, {}, r, rowIndex, colIndex, ds) : String(v);
            if(g === '' || g === '&#160;'){
                g = column.emptyGroupText || this.emptyGroupText;
            }
            return g;
        },

        // private
        getGroupField : function(){
            return this.grid.store.getGroupState();
        },

        // private
        afterRender : function(){
            if(!this.ds || !this.cm){
                return;
            }
            Ext.grid.GroupingView.superclass.afterRender.call(this);
            if(this.grid.deferRowRender){
                this.updateGroupWidths();
            }
        },

        afterRenderUI: function () {
            Ext.grid.GroupingView.superclass.afterRenderUI.call(this);

            if (this.enableGroupingMenu && this.hmenu) {
                this.hmenu.add('-',{
                    itemId:'groupBy',
                    text: this.groupByText,
                    handler: this.onGroupByClick,
                    scope: this,
                    iconCls:'x-group-by-icon'
                });

                if (this.enableNoGroups) {
                    this.hmenu.add({
                        itemId:'showGroups',
                        text: this.showGroupsText,
                        checked: true,
                        checkHandler: this.onShowGroupsClick,
                        scope: this
                    });
                }

                this.hmenu.on('beforeshow', this.beforeMenuShow, this);
            }
        },

        // private
        renderRows : function(){
            var groupField = this.getGroupField();
            var eg = !!groupField;
            // if they turned off grouping and the last grouped field is hidden
            if(this.hideGroupedColumn) {
                var colIndex = this.cm.findColumnIndex(groupField),
                    hasLastGroupField = Ext.isDefined(this.lastGroupField);
                if(!eg && hasLastGroupField){
                    this.mainBody.update('');
                    this.cm.setHidden(this.cm.findColumnIndex(this.lastGroupField), false);
                    delete this.lastGroupField;
                }else if (eg && !hasLastGroupField){
                    this.lastGroupField = groupField;
                    this.cm.setHidden(colIndex, true);
                }else if (eg && hasLastGroupField && groupField !== this.lastGroupField) {
                    this.mainBody.update('');
                    var oldIndex = this.cm.findColumnIndex(this.lastGroupField);
                    this.cm.setHidden(oldIndex, false);
                    this.lastGroupField = groupField;
                    this.cm.setHidden(colIndex, true);
                }
            }
            return Ext.grid.GroupingView.superclass.renderRows.apply(
                        this, arguments);
        },

        // private
        doRender : function(cs, rs, ds, startRow, colCount, stripe){
            if(rs.length < 1){
                return '';
            }

            if(!this.canGroup() || this.isUpdating){
                return Ext.grid.GroupingView.superclass.doRender.apply(this, arguments);
            }

            var groupField = this.getGroupField(),
                colIndex = this.cm.findColumnIndex(groupField),
                g,
                gstyle = 'width:' + this.getTotalWidth() + ';',
                cfg = this.cm.config[colIndex],
                groupRenderer = cfg.groupRenderer || cfg.renderer,
                prefix = this.showGroupName ? (cfg.groupName || cfg.header)+': ' : '',
                groups = [],
                curGroup, i, len, gid;

            for(i = 0, len = rs.length; i < len; i++){
                var rowIndex = startRow + i,
                    r = rs[i],
                    gvalue = r.data[groupField];

                    g = this.getGroup(gvalue, r, groupRenderer, rowIndex, colIndex, ds);
                if(!curGroup || curGroup.group != g){
                    gid = this.constructId(gvalue, groupField, colIndex);
                    // if state is defined use it, however state is in terms of expanded
                    // so negate it, otherwise use the default.
                    this.state[gid] = !(Ext.isDefined(this.state[gid]) ? !this.state[gid] : this.startCollapsed);
                    curGroup = {
                        group: g,
                        gvalue: gvalue,
                        text: prefix + g,
                        groupId: gid,
                        startRow: rowIndex,
                        rs: [r],
                        cls: this.state[gid] ? '' : 'x-grid-group-collapsed',
                        style: gstyle
                    };
                    groups.push(curGroup);
                }else{
                    curGroup.rs.push(r);
                }
                r._groupId = gid;
            }

            var buf = [];
            for(i = 0, len = groups.length; i < len; i++){
                g = groups[i];
                this.doGroupStart(buf, g, cs, ds, colCount);
                buf[buf.length] = Ext.grid.GroupingView.superclass.doRender.call(
                        this, cs, g.rs, ds, g.startRow, colCount, stripe);

                this.doGroupEnd(buf, g, cs, ds, colCount);
            }
            return buf.join('');
        },

        /**
         * Dynamically tries to determine the groupId of a specific value
         * @param {String} value
         * @return {String} The group id
         */
        getGroupId : function(value){
            var field = this.getGroupField();
            return this.constructId(value, field, this.cm.findColumnIndex(field));
        },

        // private
        constructId : function(value, field, idx){
            var cfg = this.cm.config[idx],
                groupRenderer = cfg.groupRenderer || cfg.renderer,
                val = (this.groupMode == 'value') ? value : this.getGroup(value, {data:{}}, groupRenderer, 0, idx, this.ds);

            return this.getPrefix(field) + Ext.util.Format.htmlEncode(val);
        },

        // private
        canGroup  : function(){
            return this.enableGrouping && !!this.getGroupField();
        },

        // private
        getPrefix: function(field){
            return this.grid.getGridEl().id + '-gp-' + field + '-';
        },

        // private
        doGroupStart : function(buf, g, cs, ds, colCount){
            buf[buf.length] = this.startGroup.apply(g);
        },

        // private
        doGroupEnd : function(buf, g, cs, ds, colCount){
            buf[buf.length] = this.endGroup;
        },

        // private
        getRows : function(){
            if(!this.canGroup()){
                return Ext.grid.GroupingView.superclass.getRows.call(this);
            }
            var r = [],
                gs = this.getGroups(),
                g,
                i = 0,
                len = gs.length,
                j,
                jlen;
            for(; i < len; ++i){
                g = gs[i].childNodes[1];
                if(g){
                    g = g.childNodes;
                    for(j = 0, jlen = g.length; j < jlen; ++j){
                        r[r.length] = g[j];
                    }
                }
            }
            return r;
        },

        // private
        updateGroupWidths : function(){
            if(!this.canGroup() || !this.hasRows()){
                return;
            }
            var tw = Math.max(this.cm.getTotalWidth(), this.el.dom.offsetWidth-this.getScrollOffset()) +'px';
            var gs = this.getGroups();
            for(var i = 0, len = gs.length; i < len; i++){
                gs[i].firstChild.style.width = tw;
            }
        },

        // private
        onColumnWidthUpdated : function(col, w, tw){
            Ext.grid.GroupingView.superclass.onColumnWidthUpdated.call(this, col, w, tw);
            this.updateGroupWidths();
        },

        // private
        onAllColumnWidthsUpdated : function(ws, tw){
            Ext.grid.GroupingView.superclass.onAllColumnWidthsUpdated.call(this, ws, tw);
            this.updateGroupWidths();
        },

        // private
        onColumnHiddenUpdated : function(col, hidden, tw){
            Ext.grid.GroupingView.superclass.onColumnHiddenUpdated.call(this, col, hidden, tw);
            this.updateGroupWidths();
        },

        // private
        onLayout : function(){
            this.updateGroupWidths();
        },

        // private
        onBeforeRowSelect : function(sm, rowIndex){
            this.toggleRowIndex(rowIndex, true);
        }
    });
    // private
    Ext.grid.GroupingView.GROUP_ID = 1000;