Missing data is a pervasive issue in real-world analytics, stemming from a multitude of factors (e.g., device malfunctions and network disruptions), making it a ubiquitous challenge in many domains. Misperception of missing data impacts decision-making and causes severe consequences. To mitigate risks from missing data and facilitate proper handling, computing methods (e.g., imputation) have been studied, which often culminate in the visual representation of data for analysts to further check. Yet, the influence of these computed representations on user judgment regarding missing data remains unclear. To study potential influencing factors and their impact on user judgment, we conducted a crowdsourcing study. We controlled 4 factors: the distribution, imputation, and visualization of missing data, and the prior knowledge of data. We compared users’ estimations of missing data with computed imputations under different combinations of these factors. Our results offer useful guidance for visualizing missing data and their imputations, which informs future studies on developing trustworthy computing methods for visual analysis of missing data.

Courses with programming assignments have long faced the issue of academic integrity violations (AIV) where cheating could harm the outcome of student learning. Checking code similarity in students' final submissions is a common way to mitigate this issue. But this single analysis is insufficient as 1) students can refactor their code to evade the check, 2) mere code similarity may not be strong enough evidence to support an AIV case, particularly for simpler assignments that may have similar solutions, and 3) code similarity cannot reveal much about the actual circumstances and behaviors of plagiarism. Due to the lack of supporting data or tools, many educators either abandon solving these challenges or rely on manual approaches that are not feasible at scale. In this paper, we propose a workflow to solve the above challenges for large programming classes by providing supporting evidence of cheating with additional learner data: detailed submission timelines with scores and source code. Running this workflow in a large advanced programming course over several years has helped us identify many cheating cases effectively and efficiently.

3D subtomogram image alignment, clustering, and segmentation are vital to macromolecular structure recognition in cryo-electron tomography (cryo-ET). However, acquiring ground-truth labels to train a unified deep learning model that can simultaneously deal with these tasks is unaffordable. To this end, we propose an end-to-end unified multi-task learning framework to simultaneously complete the three tasks, where models are trained in an unsupervised manner without using any labels. In particular, we have three parallel branches. In the alignment branch, we adopt a two-stage training scheme, i.e., self-supervised pretraining and constrained unsupervised training using our proposed skip correlation attention layer and constrained loss. Synchronously, in the clustering branch, the learned deep cluster features are utilized to iteratively cluster subtomograms into groups using pseudo-labels from an image-wise Gaussian Mixture Model (GMM). Meanwhile, in the segmentation branch, we use rough pseudo-labels generated from a voxel-wise GMM as supervision signals, and prior knowledge from humans is utilized to jointly learn how to correct these labels as well as predict reliable segmentation results. Benefiting from the end-to-end unified network architecture, our method achieves overall state-of-the-art performance on both simulated and real subtomogram processing benchmarks.

Code search is an important and frequent activity for developers using computational notebooks (e.g., Jupyter). The flexibility of notebooks brings challenges for effective code search, where classic search interfaces for traditional software code may be limited. In this paper, we propose, NBSearch, a novel system that supports semantic code search in notebook collections and interactive visual exploration of search results. NBSearch leverages advanced machine learning models to enable natural language search queries and intuitive visualizations to present complicated intra- and inter-notebook relationships in the returned results. We developed NBSearch through an iterative participatory design process with two experts from a large software company. We evaluated the models with a series of experiments and the whole system with a controlled user study. The results indicate the feasibility of our analytical pipeline and the effectiveness of NBSearch to support code search in large notebook collections.

George Michalopoulos, Yuanxin Wang, Hussam Kaka, Helen Chen, Alexander Wong. Proceedings of the 2021 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies. 2021.