How to merge cells in an extjs grid panel?

I have extjs grid.Panel and I am trying to mimic cell merging in the rows when there is duplicate data in the first column of consecutive rows. Using a column renderer, I clear a row's first column value if it is a duplicate of a previous row's value. I would like to modify the previous row's first cell's tdAttr to row span the appropriate number of rows. I cannot figure out how to get to a previous row's metaData. Below is my current renderer code.

                  renderer: function(value, metaData, record, row, col, store, gridView){                    
                     
                     var dataIndex = metaData.column.dataIndex;
                     var overrideValue = value;

                     // check previous rows and determine whether this row's first column has the same
                     // value as a previous row's first column
                     if (col == 0){
                        var i = row-1;
                        while (i >= 0 && overrideValue != ""){
                           if (store.data.items[i].get(dataIndex) == value){
                              overrideValue = "";
                              // ----- here i want to update record i's metaData...
                              // metaData.tdAttr = 'rowspan=' + row-i+1
                           } 
                           i--;     
                        }
                     }

                     return overrideValue;
                  }

I've tried a number of ways to get at the metaData associated with a record but have been unsuccessful. The getnodes and getnode methods of the gridView object return undefined.

I created the following solution. I used a combination of a column renderer and a view listener, specifically "viewready". The grid's row line is set to "false" and I use the column renderer to apply a custom style to replace the row line as appropriate and clear the appropriate cells values. I modify the background color of "merged" cells in the "viewready" listener.

<style>
.mywrapcell .x-grid-cell-inner {
   white-space: normal;
   border-top-color: #c6c6c6;
   border-top-width: 1px;
   border-top-style: solid;
}
</style>

_addGrid: function() {


      var myModel = Ext.define('User', {
        extend: 'Ext.data.Model',
        fields: [
            {name: 'col1', type: 'string'},
            {name: 'col2',  type: 'string'},
        ]
       });
   
      var myData = [{col1: 'U2', col2: 'Jan 5'},
                    {col1: 'U2', col2: 'Jan 6'},
                    {col1: 'Crowded House', col2: 'Feb 19'},
                    {col1: 'Jack Johnson', col2: 'Apr 4'},
                    {col1: 'Jack Johnson', col2: 'Apr 5'},
                    {col1: 'Cage the Elephant', col2: 'May 10'},
                    {col1: 'Cage the Elephant', col2: 'May 11'},
                    {col1: 'Blondie', col2: 'Jun 6'},
                    {col1: 'Gorillaz', col2: 'Jun 19'},
                    {col1: 'Gorillaz', col2: 'Jun 20'}];
   
      var mystore = Ext.create('Ext.data.Store', {
         model: myModel,
         data: myData,
         proxy: {
            type: 'memory',
            enablePaging: false
         }
      });

      var mygrid = Ext.create('Ext.grid.Panel', {
         store: mystore,
         itemId: 'grid',
         viewConfig:{
            listeners: {
               viewready: function(view){

                  var dataIndex = 'col1';
                  
                  // find the index of the column for row spanning
                  var colindex = view.ownerCt.columns.findIndex((x) => x.dataIndex == dataIndex);
                  
                  if (colindex != -1){
                     var viewrows = view.getNodes();
                     var bgcolor = '#fff';
                      
                     // set all the cells to the                      
                     // same background color
                     for(i=0;i<viewrows.length;i++){
                    viewrows[i].cells[colindex].style.backgroundColor = bgcolor;
                     }
                  }
            }
         },
         enableEditing: false,
         enableBulkEdit: false,
         showRowActionsColumn: false,
         enableRanking: false,
         sortableColumns: false,
         columnLines: true,
         rowLines: false, //row lines handled in renderer
         width: 225,
         columns: [
               {text: 'Artist',
                dataIndex: 'col1',
                flex: 1,
                renderer: function(value, metaData, record, row, col, store, view){                    
                      
                      var overrideValue = value;
                      
                      // check previous rows and determine whether this row's first column has the same
                      // value as a previous row's first column
                      var i = row-1;
                      
                      while (i >= 0 && overrideValue != ""){
                         if (store.data.items[i].get(metaData.column.dataIndex) == value){
                            overrideValue = '';
                         } 
                         i--;     
                      }
                      
                      if (overrideValue != ""){
                         metaData.tdCls = 'mywrapcell';
                      }
                      return overrideValue;
                }
               },
               {
                  text: 'Show Date',
                  dataIndex: 'col2',
                  tdCls: 'mywrapcell'
               }
         ],
      });
  
      this.add(mygrid);
     
 }

and the result...