/// <summary>
/// Takes an INetworkMatrix instance and composes a new INetworkMatrix instance composed of only the collection of
/// nodes given by memberNodeIds. Cost of method is (n^2 + n), where n = memberNodesIds.Count.
/// </summary>
/// <param name="socialNetworkMatrix">The social network to be searched.</param>
/// <param name="memberNodeIds">The collection of node IDs to be included in the subnetwork.</param>
/// <returns>A tuple composed of the new subnetwork, a map of original node IDs to new node IDs, and an inverse map of
/// new node IDs to original node IDs.</returns>
private static Tuple<INetworkMatrix, IDictionary<int, int>, IDictionary<int, int>> CreateSubnetworkFromNodeIds(INetworkMatrix socialNetworkMatrix, ICollection<int> memberNodeIds)
{
var subnetwork = NetworkMatrixFactory.CreateModifiableMatrix(memberNodeIds.Count);
var map = new Dictionary<int, int>(memberNodeIds.Count);
var inverseMap = new Dictionary<int, int>(memberNodeIds.Count);
var i = 1;
foreach (var nodeId in memberNodeIds)
{
map.Add(nodeId, i);
inverseMap.Add(i, nodeId);
i++;
}
foreach (var nodeId in memberNodeIds)
{
var mappedNodeId = map[nodeId];
foreach (var relatedNodeId in socialNetworkMatrix.GetNodeById(nodeId).RelatedNodes)
{
// relationships to nodes not defined in the subnetwork are ignored
if (map.ContainsKey(relatedNodeId))
subnetwork.RelateNodes(mappedNodeId, map[relatedNodeId]);
}
}
return new Tuple<INetworkMatrix, IDictionary<int, int>, IDictionary<int, int>>(subnetwork, map, inverseMap);
}
