code: function _fnGetColumns( oSettings, sParam )
  	{
  		var a = [];
  	
  		$.map( oSettings.aoColumns, function(val, i) {
  			if ( val[sParam] ) {
  				a.push( i );
  			}
  		} );
  	
  		return a;
  	}
docs: 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