I have created a histogram with matplotlib using the pyplot.hist() function. I would like to add a Poison error square root of bin height (sqrt(binheight)) to the bars. How can I do this?
The return tuple of .hist() includes return[2] -> a list of 1 Patch objects. I could only find out that it is possible to add errors to bars created via pyplot.bar().
Indeed you need to use bar. You can use to output of hist and plot it as a bar:
import numpy as np
import pylab as plt
data = np.array(np.random.rand(1000))
y,binEdges = np.histogram(data,bins=10)
bincenters = 0.5*(binEdges[1:]+binEdges[:-1])
menStd = np.sqrt(y)
width = 0.05
plt.bar(bincenters, y, width=width, color='r', yerr=menStd)
plt.show()
You can also use a combination of pyplot.errorbar() and drawstyle keyword argument. The code below creates a plot of the histogram using a stepped line plot. There is a marker in the center of each bin and each bin has the requisite Poisson errorbar.
import numpy
import pyplot
x = numpy.random.rand(1000)
y, bin_edges = numpy.histogram(x, bins=10)
bin_centers = 0.5*(bin_edges[1:] + bin_edges[:-1])
pyplot.errorbar(
bin_centers,
y,
yerr = y**0.5,
marker = '.',
drawstyle = 'steps-mid-'
)
pyplot.show()
When plotting the results of multiple histograms on the the same figure, line plots are easier to distinguish. In addition, they look nicer when plotting with a yscale='log'.
