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()
```

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 0x7f08bbbcaaf0>
```

Keywords: matplotlib code example, codex, python plot, pyplot Gallery generated by Sphinx-Gallery