How to plot result of np.histogram with matplotlib analog to plt.hist [duplicate]

Question

I like to plot my histograms like this:

data = [-0.5, 0.5, 0.5, 0.5, 
    1.5, 2.1, 2.2, 2.3, 2.4, 2.5, 3.1, 3.2]

plt.hist(data, bins=5, range=[-1, 4], histtype='step')

Now, when I have somehow large input data (larger than my memory), I need to fill the histogram chunk by chunk. E.g. like this:

H, bins = np.histogram([], bins=5, range=[-1, 4])
for data in a_lot_of_input_files:
    H += np.histogram(data, bins=5, range=[-1, 4])[0]

But the question is always, "How do I plot this H again, so it looks just like the previous matplotlib version.

The solution I came up with, looks like this:

plt.plot(bins, np.insert(H, 0, H[0]), '-', drawstyle='steps')

However, neither looks the result identical, nor does it feel very nice to create a copy of H for plotting it.

Is there some elegant solution I am missing? (I did not yet try to use plt.bar, because the bar-graphs don't work nicely, when one wants to compare histograms)

Answer 1

Not sure what you mean by "bar-graphs don't work nicely, when one wants to compare histograms",

One way to do this is with plt.bar:

import matplotlib.pyplot as plt
import numpy as np

data = [-0.5, 0.5, 0.5, 0.5, 
    1.5, 2.1, 2.2, 2.3, 2.4, 2.5, 3.1, 3.2]

plt.hist(data, bins=5, range=[-1, 4], histtype='step',edgecolor='r',linewidth=3)
H, bins = np.histogram(data[:6], bins=5, range=[-1, 4])
H+=np.histogram(data[6:], bins=5,range=[-1, 4])[0]

plt.bar(bins[:-1],H,width=1)

plt.show()

An alternative is plt.step:

import matplotlib.pyplot as plt
import numpy as np

data = [-0.5, 0.5, 0.5, 0.5, 
    1.5, 2.1, 2.2, 2.3, 2.4, 2.5, 3.1, 3.2]

plt.hist(data, bins=5, range=[-1, 4], histtype='step',edgecolor='r')
H, bins = np.histogram(data[:6], bins=5, range=[-1, 4])
H+=np.histogram(data[6:], bins=5,range=[-1, 4])[0]

bincentres = [(bins[i]+bins[i+1])/2. for i in range(len(bins)-1)]
plt.step(bincentres,H,where='mid',color='b',linestyle='--')

plt.ylim(0,6)

plt.show()

The edges don't quite extend all the way, so you might need to add a 0-bin to either end if that's a big problem for you