function _fnColumnIndexToVisible(oSettings, iMatch) {
		var aiVis = _fnGetColumns(oSettings, 'bVisible');
		var iPos = aiVis.indexOf(iMatch);

		return iPos !== -1 ? iPos : null;
	}
Convert 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