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Sometimes, by simply shuffling my data, not changing the parameters, I get a different cluster result using sklearn.DBSCAN. Why this happens?
I mean, by shuffling data, the data distribution is the same, so I should get the same result. Is this related to the implementation of DBSCAN algorithm, or internal mechanism? Thanks.
DBSCAN is not entirely deterministic, because the order in which the data are processed can change DBSCAN results. From wikipedia:
From wikipedia: "DBSCAN is not entirely deterministic: border points that are reachable from more than one cluster can be part of either cluster, depending on the order the data are processed. For most data sets and domains, this situation does not arise often and has little impact on the clustering result:[4] both on core points and noise points, DBSCAN is deterministic. DBSCAN*[8] is a variation that treats border points as noise, and this way achieves a fully deterministic result as well as a more consistent statistical interpretation of density-connected components."
Erich Schubert, Jörg Sander, Martin Ester, Hans Peter Kriegel, and Xiaowei Xu. 2017. DBSCAN Revisited, Revisited: Why and How You Should (Still) Use DBSCAN. ACM Trans. Database Syst. 42, 3, Article 19 (September 2017), 21 pages. https://doi.org/10.1145/3068335
Campello, Ricardo J. G. B.; Moulavi, Davoud; Zimek, Arthur; Sander, Jörg (2015). "Hierarchical Density Estimates for Data Clustering, Visualization, and Outlier Detection". ACM Transactions on Knowledge Discovery from Data. 10 (1): 1–51
Closely related: Why is DBSCAN deterministic?
