The problem of clustering time series data is of importance to find similar groups of time series, e.g., identifying people who share similar mobility by analyzing their spatio-temporal trajectory data as time series. YADING is one of the most recent and efficient methods to cluster large-scale time series data, which mainly consists of sampling, clustering, and assigning steps. Given a set of processed time series entities, in the sampling step, YADING clusters are found by a density-based clustering method. Next, the left input data is assigned by computing the distance (or similarity) to the entities in the sampled data. Sorted Neighbors Graph (SNG) data structure is used to prune the similarity computation of all possible pairs of entities. However, it does not guarantee to choose the sampled time series with lower density and therefore results in deterioration of accuracy. To resolve this issue, we propose a strategy to order the SNG keys with respect to the density of clusters. The strategy improves the fast selection of time series entities with lower density. The extensive experiments show that our method achieves higher accuracy in terms of NMI than the baseline YADING algorithm. The results suggest that the order of SNG keys should be the same as the clustering phase. Furthermore, the findings also show interesting patterns in identifying density radiuses for clustering.
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