Unexpected behavior from matplotlib using bar plots for floating values

Question

My code:

import matplotlib.pyplot as plt
a = [0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9]
b = [8.8913, 3.9714, 2.3416, 1.5099, 1.0078, 0.6577, 0.4198, 0.2523, 0.1141]
plt.bar(a,b)
plt.show()

I can't find a problem in this code but the graph that this outputs does not show the true values.

The output:

There are several mistakes like ,the x axis should have 0.1,0.2,0.3.,.. but it starts from -0.3? also for 0.2 the height should be around 3.9 but it is around 8 here?

Question : where have I gone wrong?

dm2 · Accepted Answer · 2021-06-30 12:08:44Z

1

You need to adjust the width of the bars (by default, the width is set to 0.8; with values as small as yours you can see why this becomes a problem).

Your data plotted with width set to 0.01 (plt.bar(a,b, width = 0.01)) looks like:

Both issues you mention are due to this width parameter. The bars in barplot are centered around their x-values, thus 0.1 is the center of the first bar (with witdh of 0.8, it spans from -0.3 to 0.5). Also, since this first bar is the tallest, it covers anything within that range (so all except the last bar are at least partially covered, due to overlap).

answered Jun 30, 2021 at 12:08

dm2

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