# Partially filled histograms in Matplotlib

Here is a recipe for plotting a histogram with its bars partially filled and partially transparent. I used this in a manuscript to show the distribution of posterior samples from a Bayesian model, and to highlight its 95% credible interval. Enjoy!

```
"""How to create a partially filled histogram.
"""
import matplotlib.pyplot as plt
from matplotlib import rcParams as defaults
from numpy.random import normal
defaults["lines.linewidth"] = 2
defaults["font.size"] = 14
if __name__ == "__main__":
y = normal(0, 1, 1000) # generate some data
fig, ax = plt.subplots(1, 1, constrained_layout=True)
ns, bins, _ = ax.hist(y, 20, histtype="step") # plot the unfilled histogram
start, stop = [-1.96, 1.96] # range to fill between
for n, l, r in zip(ns, bins, bins[1:]):
if l > start:
if r < stop:
# these bins fall completely within the range
ax.fill_between([l, r], 0, [n, n], alpha=0.5)
elif l < stop < r:
ax.fill_between([l, stop], 0, [n, n], alpha=0.5) # partial fill
elif l < start < r:
ax.fill_between([start, r], 0, [n, n], alpha=0.5) # partial fill
plt.savefig(f"../../assets/images/phist.svg", bbox_inches=0, transparent=True)
```

*Partially filled histogram.*

## Version history

- Originally posted October 03, 2019.