Multi-label active learning (MAL) aims to learn an accurate multi-label classifier by selecting which examples (or example-label pairs) will be annotated and reducing query effort. MAL is a more complicated and expensive process than single-label active learning, due to one example can be associated with a set of non-exclusive labels and the annotator has to scrutinize the whole example and label space to provide correct annotations. Instead of scrutinizing the whole example for annotation, we may just examine some of its subexamples with respect to a label for annotation. In this way, we can not only save the annotation cost but also speedup the annotation process. Given this observation, we introduce CMAL, a two-stage Cost-effective MAL strategy (CMAL) by querying subexamples. CMAL first selects the most informative example-label pairs by leveraging uncertainty, label correlation and label space sparsity. Specifically, the uncertainty of a label to an example can be reduced if its correlated labels already annotated to the example, and its uncertainty can be reduced also if more examples annotated to this label. Next, CMAL greedily queries the most probable positive subexample-label pairs of the selected example-label pair. In addition, we propose rCMAL to account for the representative of examples to more reliably select example-label pairs in the first stage. Extensive experiments on multi-label datasets from diverse domains show that our proposed CMAL and rCMAL can better save the query cost than state-of-the-art MAL methods. The contribution of leveraging label correlation, label sparsity, and representative for saving cost is also confirmed.

Active surveillance, which aims at detecting and controlling infectious diseases at an early stage, is essential to prevent the spread of infections, protect people’s health, and promote social good. One difficult problem in active surveillance is how to intelligently sample a small group of nodes as sentinels from a large number of individuals for detecting the outbreaks of infectious diseases as early as possible. To sample sentinels, the existing methods depending on the global information about a social network are infeasible for mapping out social connections is time-consuming and inaccurate. Instead, some existing studies utilize local information about individuals’ connected neighbors to heuristically select sentinels. However, few of them take into account the temporal structure of social connections, which is believed to have a direct effect on the spread of infectious diseases. In this paper, we propose two temporal-network surveillance strategies for selecting sentinels based on the friendship paradox theory, a sociological theory describing a phenomenon in social networks that most people have fewer friends than their friends have. By simulating our strategies with three existing strategies based on the susceptible-infected (SI) model, the results show that our proposed 1stAN and 2ndRN strategies can detect the outbreak of infectious diseases earlier than the other strategies on the synthetic temporal network and two real-world temporal social networks, respectively.

Multi-label active learning addresses the scarce labeled example problem by querying the most valuable unlabeled examples, or example-label pairs, to achieve a better performance with limited query cost. Current multi-label active learning methods require the scrutiny of the whole example in order to obtain its annotation. In contrast, one can find positive evidence with respect to a label by examining specific patterns (i.e., subexample), rather than the whole example, thus making the annotation process more efficient. Based on this observation, we propose a novel two-stage cost effective multi-label active learning framework, called CMAL. In the first stage, a novel example-label pair selection strategy is introduced. Our strategy leverages label correlation and label space sparsity of multi-label examples to select the most uncertain example-label pairs. Specifically, the unknown relevant label of an example can be inferred from the correlated labels that are already assigned to the example, thus reducing the uncertainty of the unknown label. In addition, the larger the number of relevant examples of a particular label, the smaller the uncertainty of the label is. In the second stage, CMAL queries the most plausible positive subexample-label pairs of the selected example-label pairs. Comprehensive experiments on multi-label datasets collected from different domains demonstrate the effectiveness of our proposed approach on cost effective queries. We also show that leveraging label correlation and label sparsity contribute to saving costs.

The goal of multiple clusterings is to discover multiple independent ways of organizing a dataset into clusters. Current approaches to this problem just focus on one-way clustering. In many real-world applications, though, it's meaningful and desirable to explore alternative two-way clustering (or co-clusterings), where both samples and features are clustered. To tackle this challenge and unexplored problem, in this paper we introduce an approach, called Multiple Co-Clusterings (MultiCC), to discover non-redundant alternative co-clusterings. MultiCC makes use of matrix tri-factorization to optimize the sample-wise and feature-wise co-clustering indicator matrices, and introduces two non-redundancy terms to enforce diversity among co-clusterings. We then combine the objective of matrix tri-factorization and two non-redundancy terms into a unified objective function and introduce an iterative solution to optimize the function. Experimental results show that MultiCC outperforms existing multiple clustering methods, and it can find interesting co-clusters which cannot be discovered by current solutions.

Current efforts on multi-label learning generally assume that the given labels of training instances are noise-free. However, obtaining noise-free labels is quite difficult and often impractical, and the presence of noisy labels may compromise the performance of multi-label learning. Partial multi-label learning (PML) addresses the scenario in which each instance is annotated with a set of candidate labels, of which only a subset corresponds to the ground-truth. The PML problem is more challenging than partial-label learning, since the latter assumes that only one label is valid and may ignore the correlation among candidate labels. To tackle the PML challenge, we introduce a feature induced PML approach called fPML, which simultaneously estimates noisy labels and trains multi-label classifiers. In particular, fPML simultaneously factorizes the observed instance-label association matrix and the instance-feature matrix into low-rank matrices to achieve coherent low-rank matrices from the label and the feature spaces, and a low-rank label correlation matrix as well. The low-rank approximation of the instance-label association matrix is leveraged to estimate the association confidence. To predict the labels of unlabeled instances, fPML learns a matrix that maps the instances to labels based on the estimated association confidence. An empirical study on public multi-label datasets with injected noisy labels, and on archived proteomic datasets, shows that fPML can more accurately identify noisy labels than related solutions, and consequently can achieve better performance on predicting labels of instances than competitive methods.

Weak-label learning is an important branch of multi-label learning; it deals with samples annotated with incomplete (weak) labels. Previous work on weak-label learning mainly considers data represented by a single view. An intuitive way to leverage multiple features obtained from different views is to concatenate the features into a single vector. However, this process is not only prone to over-fitting and often results in very high time-complexity, but also ignores the potentially useful complementary information spread across the different views. In this paper, we propose an approach based on Matrix Completion for multi-view Weak-label Learning (McWL). Matrix completion (MC) has sound theoretical properties and is robust to missing values in both feature and label spaces. Our method enforces the optimization of multiple view integration and of MC-based classification within a unified objective function. Specifically, a kernel target alignment technique and the loss function of an MC-based classifier are used to jointly and iteratively adjust the weights assigned to individual views, and to optimize the classifier. McWL can selectively integrate views and is able to assign small weights to views of low quality. Extensive experiments on a broad range of datasets validate the effectiveness of our approach against competitive algorithms.

Missing data imputation is a key issue in learning from incomplete data. Various techniques have been developed with great successes on dealing with missing values in data sets with homogeneous attributes (their independent attributes are all either continuous or discrete). This paper studies a new setting of missing data imputation, i.e., imputing missing data in data sets with heterogeneous attributes (their independent attributes are of different types), referred to as imputing mixed-attribute data sets. Although many real applications are in this setting, there is no estimator designed for imputing mixed-attribute data sets. This paper first proposes two consistent estimators for discrete and continuous missing target values, respectively. And then, a mixture-kernel-based iterative estimator is advocated to impute mixed-attribute data sets. The proposed method is evaluated with extensive experiments compared with some typical algorithms, and the result demonstrates that the proposed approach is better than these existing imputation methods in terms of classification accuracy and root mean square error (RMSE) at different missing ratios.