2D Histograms in Pure Ruby
March 18, 2026
Published on RubyStackNews
One of the most useful tools in exploratory data analysis is the 2D histogram. Not the bar chart kind — the density map kind. Given a cloud of points, it answers a simple question: where do most of them live?
This article shows how to build one from scratch in pure Ruby using ruby-libgd, replicating a classic matplotlib example — and then taking it further with real CSV data.
What is a 2D histogram?
A regular histogram divides one variable into bins and counts how many values fall in each bin. A 2D histogram does the same thing for two variables simultaneously.
The result is a grid. Each cell covers a small region of the (x, y) plane, and its color represents how many data points landed there — light for few, dark for many.
It is particularly useful when you have thousands of points and a scatter plot would just look like a solid blob. The density map reveals structure that raw scatter hides: clusters, correlations, gaps, and outliers all become visible at a glance.
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2D Histograms in Pure Ruby March 18, 2026 Published on RubyStackNews One of the most useful tools in exploratory data analysis is the 2D histogram. Not the bar chart kind — the density map kind. Gi…
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