public KnowledgeGraphLayerIDSet GetIDSet()

{
  //var map = ...
  if (map.MapType != MapType.LinkChart)
    return;

  // find the KG layer
  //var kgLayer = map.GetLayersAsFlattenedList()
  //        .OfType<KnowledgeGraphLayer>().FirstOrDefault();

  // find the first LinkChartFeatureLayer in the KG layer
  var lcFeatureLayer = kgLayer.GetLayersAsFlattenedList().OfType<LinkChartFeatureLayer>().FirstOrDefault();
  if (lcFeatureLayer != null)
    return;

  await QueuedTask.Run(() =>
  {
    // get the ID set of the KG layer
    var idSet = kgLayer.GetIDSet();

    // get the named object type in the KG that the LinkChartFeatureLayer represents
    var typeName = lcFeatureLayer.GetTypeName();
    // if there are items in the ID Set for this type
    if (idSet.Contains(typeName))
    {
      // build a new ID set containing only these records
      var dict = idSet.ToOIDDictionary();
      var oids = dict[typeName];

      var newDict = new Dictionary<string, List<long>>();
      newDict.Add(typeName, oids);

      var newIDSet = KnowledgeGraphLayerIDSet.FromDictionary(kgLayer.GetDatastore(), newDict);

      // now create a new link chart using just this subset of records
      MapFactory.Instance.CreateLinkChart("subset LinkChart", kgLayer.GetDatastore(), newIDSet);
    }
  });
}

{
        await QueuedTask.Run(() =>
{
  var idSet = kgLayer.GetIDSet();

  // is the set empty?
  var isEmpty = idSet.IsEmpty;
  // get the count of named object types
  var countNamedObjects = idSet.NamedObjectTypeCount;
  // does it contain the entity "Species";
  var contains = idSet.Contains("Species");

  // get the idSet as a dictionary of namedObjectType and oids
  var oidDict = idSet.ToOIDDictionary();
  var speciesOIDs = oidDict["Species"];

  // alternatively get the idSet as a dictionary of 
  // namedObjectTypes and uuids
  var uuidDict = idSet.ToUIDDictionary();
  var speciesUuids = uuidDict["Species"];

});
      }