Note
Click here to download the full example code
Building histograms using Rectangles and PolyCollections¶
Using a path patch to draw rectangles. The technique of using lots of Rectangle instances, or the faster method of using PolyCollections, were implemented before we had proper paths with moveto/lineto, closepoly etc in mpl. Now that we have them, we can draw collections of regularly shaped objects with homogeneous properties more efficiently with a PathCollection. This example makes a histogram -- it's more work to set up the vertex arrays at the outset, but it should be much faster for large numbers of objects.
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.patches as patches
import matplotlib.path as path
fig, ax = plt.subplots()
# Fixing random state for reproducibility
np.random.seed(19680801)
# histogram our data with numpy
data = np.random.randn(1000)
n, bins = np.histogram(data, 50)
# get the corners of the rectangles for the histogram
left = bins[:-1]
right = bins[1:]
bottom = np.zeros(len(left))
top = bottom + n
# we need a (numrects x numsides x 2) numpy array for the path helper
# function to build a compound path
XY = np.array([[left, left, right, right], [bottom, top, top, bottom]]).T
# get the Path object
barpath = path.Path.make_compound_path_from_polys(XY)
# make a patch out of it
patch = patches.PathPatch(barpath)
ax.add_patch(patch)
# update the view limits
ax.set_xlim(left[0], right[-1])
ax.set_ylim(bottom.min(), top.max())
plt.show()
![histogram path](../../_images/sphx_glr_histogram_path_001.png)
It should be noted that instead of creating a three-dimensional array and
using make_compound_path_from_polys
, we could as well create
the compound path directly using vertices and codes as shown below
nrects = len(left)
nverts = nrects*(1+3+1)
verts = np.zeros((nverts, 2))
codes = np.ones(nverts, int) * path.Path.LINETO
codes[0::5] = path.Path.MOVETO
codes[4::5] = path.Path.CLOSEPOLY
verts[0::5, 0] = left
verts[0::5, 1] = bottom
verts[1::5, 0] = left
verts[1::5, 1] = top
verts[2::5, 0] = right
verts[2::5, 1] = top
verts[3::5, 0] = right
verts[3::5, 1] = bottom
barpath = path.Path(verts, codes)
References¶
The use of the following functions, methods, classes and modules is shown in this example:
import matplotlib
matplotlib.patches
matplotlib.patches.PathPatch
matplotlib.path
matplotlib.path.Path
matplotlib.path.Path.make_compound_path_from_polys
matplotlib.axes.Axes.add_patch
matplotlib.collections.PathCollection
# This example shows an alternative to
matplotlib.collections.PolyCollection
matplotlib.axes.Axes.hist
Out:
<function Axes.hist at 0x7f280feb3af0>
Keywords: matplotlib code example, codex, python plot, pyplot Gallery generated by Sphinx-Gallery