Big idea: data can hide patterns Large biological datasets are often too big to understand by reading numbers in a table. In DREAM-High, we will eventually use heatmaps to look for patterns in breast cancer gene expression data from patients in The Cancer Genome Atlas. A heatmap can help us ask questions such as: Which samples look similar to each other? Which genes behave similarly across patients? Can visual patterns help us discover tumor subtypes? Today we will learn the same basic idea using a small practice dataset that comes with R. Main idea: A heatmap turns numbers into colors so that hidden structure becomes easier to see.