code: function _fnColumnIndexToVisible( oSettings, iMatch )
  	{
  		var aiVis = _fnGetColumns( oSettings, 'bVisible' );
  		var iPos = $.inArray( iMatch, aiVis );
  	
  		return iPos !== -1 ? iPos : null;
  	}
docs: Covert the index of an index in the data array and convert it to the visible
  column index (take account of hidden columns)
  @param {int} iMatch Column index to lookup
  @param {object} oSettings dataTables settings object
  @returns {int} i the data index
  @memberof DataTable#oApi