问题
I have a set of data that I want to show as a scatter plot. I want each point to be plotted as a square of size dx.
x = [0.5,0.1,0.3]
y = [0.2,0.7,0.8]
z = [10.,15.,12.]
dx = [0.05,0.2,0.1]
scatter(x,y,c=z,s=dx,marker='s')
The problem is that the size s that the scatter function read is in points^2. What I'd like is having each point represented by a square of area dx^2, where this area is in 'real' units, the plot units. I hope you can get this point.
I also have another question. The scatter function plots the markers with a black border, how can I drop this option and have no border at all?
回答1:
Translate from user data coordinate system to display coordinate system.
and use edgecolors='none' to plot faces with no outlines.
import numpy as np
fig = figure()
ax = fig.add_subplot(111)
dx_in_points = np.diff(ax.transData.transform(zip([0]*len(dx), dx)))
scatter(x,y,c=z,s=dx_in_points**2,marker='s', edgecolors='none')
回答2:
If you want markers that resize with the figure size, you can use patches:
from matplotlib import pyplot as plt
from matplotlib.patches import Rectangle
x = [0.5, 0.1, 0.3]
y = [0.2 ,0.7, 0.8]
z = [10, 15, 12]
dx = [0.05, 0.2, 0.1]
cmap = plt.cm.hot
fig = plt.figure()
ax = fig.add_subplot(111, aspect='equal')
for x, y, c, h in zip(x, y, z, dx):
ax.add_artist(Rectangle(xy=(x, y),
color=cmap(c**2), # I did c**2 to get nice colors from your numbers
width=h, height=h)) # Gives a square of area h*h
plt.show()
Note that:
- The squares are not centered at
(x,y). x,y are actually the coords of the square lower left. I let it this way to simplify my code. You should use(x + dx/2, y + dx/2). - The color is get from the hot colormap. I used z**2 to give colors. you should also adapt this to your needs
Finally for your second question. You can get the border of the scatter marks out using the keyword arguments edgecolor or edgecolors. These are a matplotlib color argument or a sequence of rgba tuples, respectively. If you set the parameter to 'None', borders are not draw.
回答3:
I think we can do it better with a collection of patches. According to documents:
This (PatchCollection) makes it easier to assign a color map to a heterogeneous collection of patches.
This also may improve plotting speed, since PatchCollection will draw faster than a large number of patches.
Suppose you want to plot a scatter of circles with given radius in data unit:
def circles(x, y, s, c='b', vmin=None, vmax=None, **kwargs):
"""
Make a scatter of circles plot of x vs y, where x and y are sequence
like objects of the same lengths. The size of circles are in data scale.
Parameters
----------
x,y : scalar or array_like, shape (n, )
Input data
s : scalar or array_like, shape (n, )
Radius of circle in data unit.
c : color or sequence of color, optional, default : 'b'
`c` can be a single color format string, or a sequence of color
specifications of length `N`, or a sequence of `N` numbers to be
mapped to colors using the `cmap` and `norm` specified via kwargs.
Note that `c` should not be a single numeric RGB or RGBA sequence
because that is indistinguishable from an array of values
to be colormapped. (If you insist, use `color` instead.)
`c` can be a 2-D array in which the rows are RGB or RGBA, however.
vmin, vmax : scalar, optional, default: None
`vmin` and `vmax` are used in conjunction with `norm` to normalize
luminance data. If either are `None`, the min and max of the
color array is used.
kwargs : `~matplotlib.collections.Collection` properties
Eg. alpha, edgecolor(ec), facecolor(fc), linewidth(lw), linestyle(ls),
norm, cmap, transform, etc.
Returns
-------
paths : `~matplotlib.collections.PathCollection`
Examples
--------
a = np.arange(11)
circles(a, a, a*0.2, c=a, alpha=0.5, edgecolor='none')
plt.colorbar()
License
--------
This code is under [The BSD 3-Clause License]
(http://opensource.org/licenses/BSD-3-Clause)
"""
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.patches import Circle
from matplotlib.collections import PatchCollection
if np.isscalar(c):
kwargs.setdefault('color', c)
c = None
if 'fc' in kwargs: kwargs.setdefault('facecolor', kwargs.pop('fc'))
if 'ec' in kwargs: kwargs.setdefault('edgecolor', kwargs.pop('ec'))
if 'ls' in kwargs: kwargs.setdefault('linestyle', kwargs.pop('ls'))
if 'lw' in kwargs: kwargs.setdefault('linewidth', kwargs.pop('lw'))
patches = [Circle((x_, y_), s_) for x_, y_, s_ in np.broadcast(x, y, s)]
collection = PatchCollection(patches, **kwargs)
if c is not None:
collection.set_array(np.asarray(c))
collection.set_clim(vmin, vmax)
ax = plt.gca()
ax.add_collection(collection)
ax.autoscale_view()
if c is not None:
plt.sci(collection)
return collection
All the arguments and keywords (except marker) of scatter function would work in similar way.
I've write a gist including circles, ellipses and squares/rectangles. If you want a collection of other shape, you could modify it yourself.
If you want to plot a colorbar just run colorbar() or pass the returned collection object to colorbar function.
An example:
from pylab import *
figure(figsize=(6,4))
ax = subplot(aspect='equal')
#plot a set of circle
a = arange(11)
out = circles(a, a, a*0.2, c=a, alpha=0.5, ec='none')
colorbar()
#plot one circle (the lower-right one)
circles(1, 0, 0.4, 'r', ls='--', lw=5, fc='none', transform=ax.transAxes)
xlim(0,10)
ylim(0,10)
Output:
回答4:
To make this Python 3 compatible, I added the following snippet of code
try:
basestring
except NameError:
basestring = str
from
How to check if variable is string with python 2 and 3 compatibility
This is necessary because basestring is not available in Python 3. In Python 2, the purpose of basestring was to include both str and unicode. In Python 3 there is no distinction between str and unicode, and it's just str.
来源：https://stackoverflow.com/questions/9081553/python-scatter-plot-size-and-style-of-the-marker