Methods, systems, and apparatus, including computer programs encoded on computer storage media, for detecting and localizing anomalies in large data sets. One of the methods includes identifying a user whose behavior is classified as anomalous during a particular time interval and determining observed community feature values for a community of users of which the user is a member. If observed user feature values are consistent with the observed community feature values, the behavior of the user is classified as not anomalous. If the observed user feature values are not consistent with the observed community feature values, the behavior of the user is classified as anomalous.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A computer-implemented method comprising: identifying a user whose behavior is classified as anomalous during a particular time interval; determining observed community feature values for a community of users of which the user is a member, the community of users being defined by a partition of users in a user graph for the particular time interval, the user graph having nodes that represent distinct users and edges that represent relationships between users from user behavior of the users in the particular time interval; determining observed user feature values of the user during the particular time interval from the user graph for the particular time interval; determining whether the observed user feature values are consistent with the observed community feature values; classifying the behavior of the user as not anomalous when the observed user feature values are consistent with the observed community feature values; and classifying the behavior of the user as anomalous when the observed user feature values are not consistent with the observed community feature values. 2. The method of claim 1, further comprising: determining that the observed user feature values of the user are not consistent with predicted user feature values of the user for the particular time interval. 3. The method of claim 1, further comprising: generating a community model using aggregate community feature values computed from a community graph having nodes that each represent a partition of a respective user graph within one of multiple time intervals, the community graph having edges between nodes that represent matching partitions of respective user graphs across adjacent time intervals, each user graph having nodes that represent distinct users and having edges that represent relationships between users from user behavior of the users in a particular time interval; determining predicted community feature values for the community, the predicted community feature values being generated by the community model; and determining that the predicted community feature values are consistent with the observed community feature values. 4. The method of claim 1, further comprising: generating a user model using user feature values of a node representing the user in one or more of the user graphs; and determining predicted user feature values for the user using the user model, wherein identifying a user whose behavior is classified as anomalous during a particular time interval comprises determining that the observed user feature values during the particular time interval are not consistent with the predicted user feature values during the particular time interval. 5. The method of claim 1, wherein determining whether the observed user feature values are consistent with the observed community feature values comprises: computing a vector distance between a first vector having the predicted observed user feature values and a second vector having the observed community feature values; and determining whether the vector distance satisfies a threshold. 6. The method of claim 1, wherein determining whether the observed user feature values are consistent with the observed community feature values comprises: generating a ranking of users according to a respective vector distance for each user, the vector distance for each user representing a measure of consistency of observed user feature values for the user with observed feature values of the user's respective community; and determining that the vector distance for the user is within a number of top-ranked users having the largest vector distances. 7. A computer-implemented method comprising: receiving data representing aggregate community feature values of a community of users over time, the aggregate community feature values being computed from a community graph having nodes that each represent a partition of a respective user graph within one of multiple time intervals, the community graph having edges between nodes that represent matching partitions of respective user graphs from adjacent time intervals, each user graph having nodes that represent distinct users and edges that represent relationships between users from user behavior of the users in a particular time interval; determining predicted community feature values for the community, the predicted community feature values being generated by a community model trained on the aggregate community feature values of the community of users over time; determining that the predicted community feature values are not consistent with observed community feature values during a most recent time interval; and in response to determining that the predicted community feature values are not consistent with observed community feature values during a most recent time interval, classifying behavior of the community as anomalous during the most recent time interval. 8. The method of claim 7, wherein determining that the predicted community feature values are not consistent with observed community feature values during a most recent time interval comprises: computing a vector distance between a first vector having the predicted community feature values and a second vector having the observed community feature values; and determining that the vector distance satisfies a threshold. 9. The method of claim 8, wherein determining that the predicted community feature values are not consistent with observed community feature values during a most recent time interval comprises: generating a ranking of communities according to a respective vector distance for each community; and determining that the vector distance for the community is within a number of top-ranked communities having the largest vector distances. 10. The method of claim 7, further comprising computing the aggregate community feature values from individual user feature values of distinct users in the community. 11. The method of claim 10, wherein computing the aggregate community feature values comprises computing aggregate community feature values from multiple partitions of user nodes within a particular time interval, the multiple partitions being represented by nodes of a subgraph representing the community in the community graph. 12. A system comprising: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: identifying a user whose behavior is classified as anomalous during a particular time interval; determining observed community feature values for a community of users of which the user is a member, the community of users being defined by a partition of users in a user graph for the particular time interval, the user graph having nodes that represent distinct users and edges that represent relationships between users from user behavior of the users in the particular time interval; determining observed user feature values of the user during the particular time interval from the user graph for the particular time interval; determining whether the observed user feature values are consistent with the observed community feature values; classifying the behavior of the user as not anomalous when the observed user feature values are consistent with the observed community feature values; and classifying the behavior of the user as anomalous when the observed user feature values are not consistent with the observed community feature values. 13. The system of claim 12, wherein the operations further comprise: determining that the observed user feature values of the user are not consistent with predicted user feature values of the user for the particular time interval. 14. The system of claim 12, wherein the operations further comprise: generating a community model using aggregate community feature values computed from a community graph having nodes that each represent a partition of a respective user graph within one of multiple time intervals, the community graph having edges between nodes that represent matching partitions of respective user graphs across adjacent time intervals, each user graph having nodes that represent distinct users and having edges that represent relationships between users from user behavior of the users in a particular time interval; determining predicted community feature values for the community, the predicted community feature values being generated by the community model; and determining that the predicted community feature values are consistent with the observed community feature values. 15. The system of claim 12, wherein the operations further comprise: generating a user model using user feature values of a node representing the user in one or more of the user graphs; and determining predicted user feature values for the user using the user model, wherein identifying a user whose behavior is classified as anomalous during a particular time interval comprises determining that the observed user feature values during the particular time interval are not consistent with the predicted user feature values during the particular time interval. 16. The system of claim 12, wherein determining whether the observed user feature values are consistent with the observed community feature values comprises: computing a vector distance between a first vector having the predicted observed user feature values and a second vector having the observed community feature values; and determining whether the vector distance satisfies a threshold. 17. The system of claim 12, wherein determining whether the observed user feature values are consistent with the observed community feature values comprises: generating a ranking of users according to a respective vector distance for each user, the vector distance for each user representing a measure of consistency of observed user feature values for the user with observed feature values of the user's respective community; and determining that the vector distance for the user is within a number of top-ranked users having the largest vector distances.