Adding an index to a DocumentDB collection

IndexDocDB.cs

DocumentClient client;
client = new DocumentClient(new Uri(endpointUri), primaryKey);

DocumentCollection resultCollection = client.ReadDocumentCollectionAsync(UriFactory.CreateDocumentCollectionUri(databaseName, collectionName)).Result;
resultCollection.Id = collectionName;
resultCollection.IndexingPolicy.IncludedPaths.Clear();
resultCollection.IndexingPolicy.IncludedPaths.Add(
    new IncludedPath
    {
        Path = "/timestamp/?",
        Indexes = new Collection<Index> {
            new RangeIndex(DataType.String) { Precision = -1 }
        }
    });
resultCollection.IndexingPolicy.IncludedPaths.Add(
    new IncludedPath
    {
        Path = "/*",
        Indexes = new Collection<Index> {
            new HashIndex(DataType.String) { Precision = 3 },
            new RangeIndex(DataType.Number) { Precision = -1 }
        },
    });

client.ReplaceDocumentCollectionAsync(resultCollection).Wait();