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Feature stack base #1671

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Jan 27, 2013
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2 changes: 2 additions & 0 deletions 2 CHANGELOG
Original file line number Diff line number Diff line change
@@ -1,5 +1,7 @@
2013-01-07 Add framealpha keyword argument to legend - PO

2013-01-16 Till Stensitzki added a baseline feature to stackplot

2012-12-22 Added classes for interpolation within triangular grids
(LinearTriInterpolator) and to find the triangles in which points
lie (TrapezoidMapTriFinder) to matplotlib.tri module. - IMT
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7 changes: 7 additions & 0 deletions 7 doc/users/whats_new.rst
Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,13 @@ revision, see the :ref:`github-stats`.
new in matplotlib-1.3
=====================

Baselines for stackplot
-----------------------
Till Stensitzki added non-zero baselines to :func:`~matplotlib.pyplot.stackplot`.
They may be symmetric or weighted.

.. plot:: mpl_examples/pylab_examples/stackplot_demo2.py

Initialize a rotated rectangle
------------------------------
Damon McDougall extended the :class:`~matplotlib.patches.Rectangle` constructor
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26 changes: 26 additions & 0 deletions 26 examples/pylab_examples/stackplot_demo2.py
Original file line number Diff line number Diff line change
@@ -0,0 +1,26 @@
import numpy as np
import matplotlib.pyplot as plt

np.random.seed(0)
def layers(n, m):
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I know its only an example, but a docstring would be nice here - something which focuses on the purpose of the function, rather than its args/kwargs.

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Actually, this is not uncommon to do in the examples. IIRC, the sphinx
doc-builder will take the docstring portion of the example, and render it
as ReST text above the source code portion. If one feels like having a
docstring there, feel free. The more the better.

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Sure thing :)

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Explanation of the code:
This is just a direct copy of the original code. All it does is calculating random Gaussians.

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Done in bd204e1.

"""
Return *n* random Gaussian mixtures, each of length *m*.
"""
def bump(a):
x = 1 / (.1 + np.random.random())
y = 2 * np.random.random() - .5
z = 10 / (.1 + np.random.random())
for i in range(m):
w = (i / float(m) - y) * z
a[i] += x * np.exp(-w * w)
a = np.zeros((m, n))
for i in range(n):
for j in range(5):
bump(a[:, i])
return a

d = layers(3, 100)

plt.subplots()
plt.stackplot(range(100), d.T, baseline='wiggle')
plt.show()
54 changes: 49 additions & 5 deletions 54 lib/matplotlib/stackplot.py
Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,16 @@ def stackplot(axes, x, *args, **kwargs):

Keyword arguments:

*baseline* : ['zero', 'sym', 'wiggle', 'weighted_wiggle']
Method used to calculate the baseline. 'zero' is just a
simple stacked plot. 'sym' is symmetric around zero and
is sometimes called `ThemeRiver`. 'wiggle' minimizes the
sum of the squared slopes. 'weighted_wiggle' does the
same but weights to account for size of each layer.
It is also called `Streamgraph`-layout. More details
can be found at http://www.leebyron.com/else/streamgraph/.


*colors* : A list or tuple of colors. These will be cycled through and
used to colour the stacked areas.
All other keyword arguments are passed to
Expand All @@ -44,17 +54,51 @@ def stackplot(axes, x, *args, **kwargs):
if colors is not None:
axes.set_color_cycle(colors)

baseline = kwargs.pop('baseline', 'zero')
# Assume data passed has not been 'stacked', so stack it here.
y_stack = np.cumsum(y, axis=0)
stack = np.cumsum(y, axis=0)

r = []
if baseline == 'zero':
first_line = 0.

elif baseline == 'sym':
first_line = -np.sum(y, 0) * 0.5
stack += first_line[None, :]

elif baseline == 'wiggle':
m = y.shape[0]
first_line = (y * (m - 0.5 - np.arange(0, m)[:, None])).sum(0)
first_line /= -m
stack += first_line

elif baseline == 'weighted_wiggle':
m, n = y.shape
center = np.zeros(n)
total = np.sum(y, 0)
increase = np.hstack((y[:, 0:1], np.diff(y)))
below_size = total - stack
below_size += 0.5 * y
move_up = below_size / total
move_up[:, 0] = 0.5
center = (move_up - 0.5) * increase
center = np.cumsum(center.sum(0))
first_line = center - 0.5 * total
stack += first_line
else:
errstr = "Baseline method %s not recognised. " % baseline
errstr += "Expected 'zero', 'sym', 'wiggle' or 'weighted_wiggle'"
raise ValueError(errstr)

# Color between x = 0 and the first array.
r.append(axes.fill_between(x, 0, y_stack[0, :],
facecolor=axes._get_lines.color_cycle.next(), **kwargs))
r.append(axes.fill_between(x, first_line, stack[0, :],
facecolor=axes._get_lines.color_cycle.next(),
**kwargs))

# Color between array i-1 and array i
for i in xrange(len(y) - 1):
r.append(axes.fill_between(x, y_stack[i, :], y_stack[i + 1, :],
facecolor=axes._get_lines.color_cycle.next(), **kwargs))
color = axes._get_lines.color_cycle.next()
r.append(axes.fill_between(x, stack[i, :], stack[i + 1, :],
facecolor= color,
**kwargs))
return r
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