Datatable: How to get column header value for the cell

In datatable how to get the value of column header of the cell.
I am using the following code snippet to get column and row ID’s

 var columnId = grid.getSelectedId().column;   // output value : data6  										
 var rowId = grid.getSelectedId().row;  // output value : 1390307879906  
 grid.getItem(rowId);
 grid.getItem(columnId); // not working

How to get the values corresponding to the columns ?

You can use getColumnConfig
http://docs.webix.com/api__ui.datatable_getcolumnconfig.html

var column = grid.getColumnConfig(columnId)
var header = column.header[0]; // 0 - index of header row for multiline columns

Do I have to iterate whole header. I have very large number of header columns around 3000 and I need header corresponding to selected cell.
so when on selected cell I call grid.getSelectedId().column; I get the id of header in my case it is ‘data6’. So now how to get the text value of the header from the id.

If you have a single line header

var label = grid.getColumnConfig(columnId).header[0].text;

If you have a multiline(or single line) header

var header = grid.getColumnConfig(columnId).header;
var label = header[header.length - 1].text;

In both cases you need not iterate through all columns. There is method which return column configuration by column id ( grid.getSelectedId().column ) and from column configuration you can read the text of header.