function _fnGetColumns(oSettings, sParam) {
		var a = [];

		oSettings.aoColumns.map(function (val, i) {
			if (val[sParam]) {
				a.push(i);
			}
		});

		return a;
	}
Get an array of column indexes that match a given property
 @param {object} oSettings dataTables settings object
 @param {string} sParam Parameter in aoColumns to look for - typically
   bVisible or bSearchable
 @returns {array} Array of indexes with matched properties
 @memberof DataTable#oApi