Issue with plotting multiple histograms on the same plot

Question

I need to plot several histograms on the same plot. I like the display the following code generates:

import random
import numpy
from matplotlib import pyplot

x = [random.gauss(3,1) for _ in range(400)]
y = [random.gauss(4,2) for _ in range(400)]

bins = numpy.linspace(-10, 10, 100)

pyplot.hist(x, bins, alpha=0.5)
pyplot.hist(y, bins, alpha=0.5)
pyplot.show()

This code was mentioned on this page:Plot two histograms at the same time with matplotlib Basically I am having trouble plotting the same kind of histograms but for data that looks like:

y1=[20,33,54,34,22]
x1=[0,2,4,6,8]
y2=[28,31,59,14,12]
x2=[0,2,4,6,8]

Using the aforementioned code I could not get the y axis to go above 2.0 strange but I must be making a foolish mistake.

Thanks.

Really hard to guess, since this code should work. I would try eliminating different plots (comment out y or x plot) and see if you can narrow down the source of the problem. — Radio-
– Radio-, Commented Mar 2, 2013 at 8:08
Maybe you should look at the definition of hist. If your bins are those in x1 it is normal you get nothing from the values in y1 — joaquin
– joaquin, Commented Mar 2, 2013 at 8:51
I have a feeling this only works with randomly generated data(as seen from the examples on this site) but surely that can't be the case. — shokan
– shokan, Commented Mar 2, 2013 at 8:51
No, random data is used as an example. hist works for any kind of integer or float data. The problem is you are not applying hist correctly. for your data probably you want to use a bar plot — joaquin
– joaquin, Commented Mar 2, 2013 at 8:53
@joaquin I am unable to get the correct histogram for even a single data set: import pyfits, numpy, math, pylab, scipy.optimize, time import matplotlib import matplotlib.pyplot as plt from mpl_toolkits.mplot3d import Axes3D from scipy import optimize from scipy.optimize import leastsq from lmfit import minimize, Parameters from numpy import * from matplotlib import pyplot x = numpy.array([11,2,3,14,5]) #y = numpy.array([24,33,56,21,99]) print(x) #print(y) bins =[0,2,4,6,8] pyplot.hist(x,bins) #pyplot.hist(y, bins) pyplot.show() — shokan
– shokan, Commented Mar 2, 2013 at 8:54

joaquin · Accepted Answer · 2013-03-02 09:06:26Z

1

Probably you are looking for this:

 pyplot.bar(x2,y2, color='b', width=2, alpha=0.5)
 pyplot.bar(x1,y1, color='r', width=2, alpha=0.5)
 pyplot.show()

enter image description here

answered Mar 2, 2013 at 9:06

joaquin

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4 Comments

shokan Over a year ago

it works except that I see three colours instead of just two. Too much hassle for such a simple task.

tacaswell Over a year ago

@shokan what do you mean 'three colors'? If you overlay two things with alpha < 1 you must get three colors. The alpha kwarg is an artist kwarg so all of the plotting functions should respect it.

shokan Over a year ago

@tcaswell but you see when I include legends on to the plot it only serves as a key for the two data sets while you see three colours on the plot. Hence why is it that in some places pink and blue are used and in other you have a pink and a combination of pink and blue used. It is hard to differentiate.

tacaswell Over a year ago

@shokan You are overlaying two transparent colors. If you don't want this, set alpha=1, but then you won't be able to see the back bar when it is smaller.

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