Hi there, I'm sorry to ask such a newbie question, but I'd like to format a custom box plot and although there are numerous examples on the web and tons of docstrings in matplotlib, I'm stuck somehow. My problems center around axes / spines. In detail, my problems are:
1) I want an y-axis on the left that spans from -0.6 to 1.1, ends in an arrow, has major ticks at 0 and 1 and minor ticks at [0.1...0.9] As far as I understand, there is no option to let spines end in an arrow head, so I have to draw the myself. I get the ticks to appear at the right positions and the y-range to be as desired - however, the spine line is not drawn over the full y-range, but only where there is data in the diagram. Also, I copied the arrow annotation code blindly from an older post on this list, but do not understand how I can adapt the arrow head to appear at a data position (instead of at the corner of the Axes area). One problem is, that I get ticks on the right although that spine was disabled. 2) I want some kind of x-axis at y==0, without ticks and without arrow Using some methods on the spines, I can disable the top spine and move the bottom spine to zero. However, as with the y-axis, I cannot control from where to where the line itself is drawn. As attachments, you'll find a hand sketch of what my graph should look like and matplotlib code that goes nearly all the way. I would be very happy about a hint on how to fix the problems left. Thanks an advance, Mark [cid:ed2f1b56-2e4e-4cb3-9a9e-4b2b2388781b@exch.iais.fraunhofer.de]
<<inline: boxplot_sketch.png>>
#! /usr/bin/env python
"""Example code for custom box diagram
2012-06-15, mark.asb...@iais.fraunhofer.de
"""
import numpy
from matplotlib import pylab
def draw_bars(data, descriptions=None, colors=None, reverse_coords=False, position=0, axes=pylab):
# if no descriptions are given, use data to annotate itself
if descriptions == None:
descriptions = data
# if no colors are given, all boxes will be white
if colors == None:
colors = len(data) * ('white',)
# sort data for finding y centers and drawing in right order
assert numpy.all(numpy.array(data) >= 0)
idx = numpy.argsort(data)[::-1]
data = numpy.array(data)[idx]
descriptions = numpy.array(descriptions)[idx]
colors = numpy.array(colors)[idx]
# reverse y-position if desired
if reverse_coords:
data = -data
# draw boxes
for top, color in zip (data, colors):
axes.bar (position + 0.2, top, 0.4, color=color)
# put labels on boxes
tops = data.tolist()
bots = data.tolist()[1:] + [0,]
for top, bottom, description in zip(tops, bots, descriptions):
axes.text (position + 0.4, 0.5 * (top + bottom), description,
horizontalalignment='center', verticalalignment='center')
def draw_dataset(dataset, titles=None, descriptions=None, colors=None, axes=pylab):
# ensure data is in numpy format
dataset = numpy.require(dataset, dtype=float)
titles = numpy.require(titles, dtype=str)
descriptions = numpy.require(descriptions, dtype=str)
# draw bar by bar, separating positive from negative values
position = 0
for row, descr in zip(dataset, descriptions):
row_data = numpy.array(row)
descr_data = numpy.array (descr)
positives = numpy.array(row) > 0
draw_bars( row_data[ positives], descr_data[ positives], colors, False, position, axes)
draw_bars(-row_data[-positives], descr_data[-positives], colors, True, position, axes)
position += 1
# finally, but title above bars
if titles != None:
for position, title in enumerate(titles):
axes.text (position + 0.4, 1.1, title,
horizontalalignment='center', verticalalignment='center')
# create new figure
fig = pylab.figure()
ax = fig.add_subplot(1,1,1)
# plot my data
datasets = [(0.8, 0.6, 0.4, -0.2),
(0.7, 0.5, 0.3, -0.3)]
descriptions = [('A', 'B', 'C', 'D'),
('A\'', 'B\'', 'C\'', 'D\'')]
colors = ['0.3', '0.5', '0.75', '0.1']
draw_dataset(datasets, ['Some Text\nLines', 'Other Text'], descriptions, colors, ax)
# use left spine and x-axis at zero
ax.spines['left'].set_position('zero')
ax.spines['left'].set_smart_bounds(True)
ax.spines['bottom'].set_position('zero')
ax.spines['bottom'].set_smart_bounds(True)
ax.spines['right'].set_color('none')
ax.spines['top'].set_color('none')
# try to add arrow to left spine
# (http://www.mailinglistarchive.com/html/matplotlib-users@lists.sourceforge.net/2011-02/msg00065.html)
al = 7 # arrow length in points
arrowprops=dict(clip_on=False, # plotting outside axes on purpose
frac=1., # make end arrowhead the whole size of arrow
headwidth=al, # in points
facecolor='k')
kwargs = dict(
xycoords='axes fraction',
textcoords='offset points',
arrowprops= arrowprops,
)
ax.annotate("",(0,1),xytext=(0,-al), **kwargs) # left spin arrow
# format rest of figure
pylab.ylabel('Rate')
pylab.yticks(numpy.arange(0.0, 1.1, 0.1)) #, ['%d' % val for val in vals])
pylab.xticks([])
ax.set_ylim(-0.6, 1.4)
ax.set_xlim( 0.0, 2.0)
ax.set_aspect('equal')
pylab.title('Diagram Title')
# done
pylab.show()
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