  Modern machine learning models are becoming increasingly expensive to train
for real-world image and text classification tasks, where massive web-scale
data is collected in a streaming fashion. To reduce the training cost, online
batch selection techniques have been developed to choose the most informative
datapoints. However, these techniques can suffer from poor worst-class
generalization performance due to class imbalance and distributional shifts.
This work introduces REDUCR, a robust and efficient data downsampling method
that uses class priority reweighting. REDUCR reduces the training data while
preserving worst-class generalization performance. REDUCR assigns priority
weights to datapoints in a class-aware manner using an online learning
algorithm. We demonstrate the data efficiency and robust performance of REDUCR
on vision and text classification tasks. On web-scraped datasets with
imbalanced class distributions, REDUCR significantly improves worst-class test
accuracy (and average accuracy), surpassing state-of-the-art methods by around
15%.
