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SF.net SVN: matplotlib:[8769] branches/v1_0_maint/doc/users
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From: <jd...@us...> - 2010-11-04 18:28:09
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Revision: 8769
http://matplotlib.svn.sourceforge.net/matplotlib/?rev=8769&view=rev
Author: jdh2358
Date: 2010-11-04 18:28:03 +0000 (Thu, 04 Nov 2010)
Log Message:
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added recipes
Modified Paths:
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branches/v1_0_maint/doc/users/index.rst
Added Paths:
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branches/v1_0_maint/doc/users/recipes.rst
Modified: branches/v1_0_maint/doc/users/index.rst
===================================================================
--- branches/v1_0_maint/doc/users/index.rst 2010-11-01 13:05:41 UTC (rev 8768)
+++ branches/v1_0_maint/doc/users/index.rst 2010-11-04 18:28:03 UTC (rev 8769)
@@ -27,6 +27,7 @@
transforms_tutorial.rst
path_tutorial.rst
annotations_guide.rst
+ recipes.rst
toolkits.rst
screenshots.rst
whats_new.rst
Added: branches/v1_0_maint/doc/users/recipes.rst
===================================================================
--- branches/v1_0_maint/doc/users/recipes.rst (rev 0)
+++ branches/v1_0_maint/doc/users/recipes.rst 2010-11-04 18:28:03 UTC (rev 8769)
@@ -0,0 +1,224 @@
+.. _recipes:
+
+********************
+Our Favorite Recipes
+********************
+
+Here is a collection of short tutorials, examples and code snippets
+that illustrate some of the useful idioms and tricks to make snazzier
+figures and overcome some matplotlib warts.
+
+Fixing common date annoyances
+=============================
+
+matplotlib allows you to natively plots python datetime instances, and
+for the most part does a good job picking tick locations and string
+formats. There are a couple of things it does not handle so
+gracefully, and here are some tricks to help you work around them.
+We'll load up some sample date data which contains datetime.date
+objects in a numpy record array::
+
+ In [63]: datafile = cbook.get_sample_data('goog.npy')
+
+ In [64]: r = np.load(datafile).view(np.recarray)
+
+ In [65]: r.dtype
+ Out[65]: dtype([('date', '|O4'), ('', '|V4'), ('open', '<f8'), ('high', '<f8'), ('low', '<f8'), ('close', '<f8'), ('volume', '<i8'), ('adj_close', '<f8')])
+
+ In [66]: r.date
+ Out[66]:
+ array([2004-08-19, 2004-08-20, 2004-08-23, ..., 2008-10-10, 2008-10-13,
+ 2008-10-14], dtype=object)
+
+The dtype of the numpy record array for the field 'date' is '|O4'
+which means it is a 4-byte python object pointer; in this case the
+objects are datetime.date instances, which we can see when we print
+some samples in the ipython terminal window.
+
+If you plot the data, you will see that the x tick labels are all
+squashed together::
+
+ In [67]: plot(r.date, r.close)
+ Out[67]: [<matplotlib.lines.Line2D object at 0x92a6b6c>]
+
+.. plot::
+
+ import matplotlib.cbook as cbook
+ datafile = cbook.get_sample_data('goog.npy')
+ r = np.load(datafile).view(np.recarray)
+ plt.figure()
+ plt.plot(r.date, r.close)
+ plt.show()
+
+Another annoyance is that if you hover the mouse over a the window and
+look in the lower right corner of the matplotlib toolbar at the x and
+y coordinates, you see that the x locations are formatted the same way
+the tick labels are, eg "Dec 2004". What we'd like is for the
+location in the toolbar to have a higher degree of precision, eg
+giving us the exact date out mouse is hovering over. To fix the first
+problem, we can use method:`matplotlib.figure.Figure.autofmt_xdate()`
+and to fix the second problem we can use the ``ax.fmt_xdata``
+attribute which can be set to any function that takes a position and
+returns a string. matplotlib has a number of date formatters built
+im, so we'll use one of those.
+
+.. plot::
+
+
+ import matplotlib.cbook as cbook
+ datafile = cbook.get_sample_data('goog.npy')
+ r = np.load(datafile).view(np.recarray)
+ fig, ax = plt.subplots(1)
+ ax.plot(r.date, r.close)
+
+ # rotate and align the tick labels so they look better
+ fig.autofmt_xdate()
+
+ # use a more precise date string for the x axis locations in the
+ # toolbar
+ import matplotlib.dates as mdates
+ ax.fmt_xdata = mdates.DateFormatter('%Y-%m-%d')
+
+
+
+Fill Between and Alpha
+======================
+
+The :method:`~matplotlib.axes.Axes.fill_between` function generates a
+shaded region between a min and max boundary that is useful for
+illustrating ranges. It has a very handy ``where`` argument to
+combine filling with logical ranges, eg to just fill in a curve over
+some threshold value.
+
+At it's most basic level, ``fill_between`` can be use to enhance a
+graphs visual appearance. Let's compare two graphs of a financial
+times with a simple line plot on the left and a filled line on the
+right.
+
+.. plot::
+ :include-source:
+
+ import matplotlib.cbook as cbook
+
+ # load up some sample financial data
+ datafile = cbook.get_sample_data('goog.npy')
+ r = np.load(datafile).view(np.recarray)
+
+ # create two subplots with the shared x and y axes
+ fig, (ax1, ax2) = plt.subplots(1,2, sharex=True, sharey=True)
+
+ pricemin = r.close.min()
+
+ ax1.plot(r.date, r.close, lw=2)
+ ax2.fill_between(r.date, pricemin, r.close, facecolor='blue', alpha=0.5)
+
+ for ax in ax1, ax2:
+ ax.grid(True)
+
+ ax1.set_ylabel('price')
+ fig.suptitle('Google (GOOG) daily closing price')
+ fig.autofmt_xdate()
+ plt.show()
+
+The alpha channel is not necessary here, but it can be used to soften
+colors for more visually appealing plots. In other examples, as we'll
+see below, the alpha channel is functionally useful as the shaded
+regions can overlap and alpha allows you to see both. Note that the
+postscript format does not support alpha (this is a postscript
+limitation, not a matplotlib limitation), so when using alpha save
+your figures in PNG, PDF or SVG.
+
+Our next example computes two populations of random walkers with a
+different mean and standard deviation of the normal distributions from
+which there steps are drawn. We use shared regions to plot +/- one
+standard deviation of the mean position of the population. Here the
+alpha channel is useful, not just aesthetic.
+
+.. plot::
+ :include-source:
+
+ Nsteps, Nwalkers = 100, 250
+ t = np.arange(Nsteps)
+
+ # an Nsteps x Nwalkers array of random walk steps
+ S1 = 0.002 + 0.01*np.random.randn(Nsteps, Nwalkers)
+ S2 = 0.004 + 0.02*np.random.randn(Nsteps, Nwalkers)
+
+ # an Nsteps x Nwalkers array of random walker positions
+ X1 = S1.cumsum(axis=0)
+ X2 = S2.cumsum(axis=0)
+
+
+ # Nsteps length arrays empirical means and standard deviations of both
+ # populations over time
+ mu1 = X1.mean(axis=1)
+ sigma1 = X1.std(axis=1)
+ mu2 = X2.mean(axis=1)
+ sigma2 = X2.std(axis=1)
+
+ # plot it!
+ fig, ax = plt.subplots(1)
+ ax.plot(t, mu1, lw=2, label='mean population 1', color='blue')
+ ax.plot(t, mu1, lw=2, label='mean population 2', color='yellow')
+ ax.fill_between(t, mu1+sigma1, mu1-sigma1, facecolor='blue', alpha=0.5)
+ ax.fill_between(t, mu2+sigma2, mu2-sigma2, facecolor='yellow', alpha=0.5)
+ ax.set_title('random walkers empirical $\mu$ and $\pm \sigma$ interval')
+ ax.legend(loc='upper left')
+ ax.set_xlabel('num steps')
+ ax.set_ylabel('position')
+ ax.grid()
+ plt.show()
+
+
+
+The where keyword argument is very handy for highlighting certain
+regions of the graph. Where takes a boolean mask the same length as
+the x, ymin and ymax arguments, and only fills in the region where the
+boolean mask is True. In the example below, we take a a single random
+walker and compute the analytic mean and standard deviation of the
+population positions. The population mean is shown as the black
+dashed line, and the plus/minus one sigma deviation from the mean is
+showsn as the yellow filled region. We use the where mask
+``X>upper_bound`` to find the region where the walker is above the
+one sigma boundary, and shade that region blue.
+
+.. plot::
+ :include-source:
+
+ np.random.seed(1234)
+
+ Nsteps = 500
+ t = np.arange(Nsteps)
+
+ mu = 0.002
+ sigma = 0.01
+
+ # the steps and position
+ S = mu + sigma*np.random.randn(Nsteps)
+ X = S.cumsum()
+
+ # the 1 sigma upper and lower population bounds
+ lower_bound = mu*t - sigma*np.sqrt(t)
+ upper_bound = mu*t + sigma*np.sqrt(t)
+
+ fig, ax = plt.subplots(1)
+ ax.plot(t, X, lw=2, label='walker position', color='blue')
+ ax.plot(t, mu*t, lw=1, label='population mean', color='black', ls='--')
+ ax.fill_between(t, lower_bound, upper_bound, facecolor='yellow', alpha=0.5,
+ label='1 sigma range')
+ ax.legend(loc='upper left')
+
+ # here we use the where argument to only fill the region where the
+ # walker is above the population 1 sigma boundary
+ ax.fill_between(t, upper_bound, X, where=X>upper_bound, facecolor='blue', alpha=0.5)
+ ax.set_xlabel('num steps')
+ ax.set_ylabel('position')
+ ax.grid()
+ plt.show()
+
+
+Another handy use of filled regions is to highlight horizontal or
+vertical spans of an axes -- for that matplotlib has some helper
+functions :method:`~matplotlib.axes.Axes.axhspan` and
+:method:`~matplotlib.axes.Axes.axvspan` and example
+:ref:`pylab_examples-axhspan_demo`.
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