added example to show errorbar subsampling and extended the doc as well as the validity check for errorevery keyword of errorbar.

chrodan · chrodan · commit b674fc19f3b2 · 2012-02-29T10:59:00.000+01:00
diff --git a/CHANGELOG b/CHANGELOG
@@ -1,3 +1,6 @@
+2012-02-29 errorevery keyword added to errorbar to enable errorbar
+           subsampling. fixes issue #600.
+
 2011-12-29 ps and pdf markers are now stroked only if the line width
            is nonzero for consistency with agg, fixes issue #621. - JKS
 
diff --git a/examples/pylab_examples/errorbar_subsample.py b/examples/pylab_examples/errorbar_subsample.py
@@ -0,0 +1,30 @@
+'''
+Demo for the errorevery keyword to show data full accuracy data plots with
+few errorbars.
+'''
+
+import numpy as np
+import matplotlib.pyplot as plt
+
+# example data
+x = np.arange(0.1, 4, 0.1)
+y = np.exp(-x)
+
+# example variable error bar values
+yerr = 0.1 + 0.1*np.sqrt(x)
+
+
+# Now switch to a more OO interface to exercise more features.
+fig, axs = plt.subplots(nrows=1, ncols=2, sharex=True)
+ax = axs[0]
+ax.errorbar(x, y, yerr=yerr)
+ax.set_title('all errorbars')
+
+ax = axs[1]
+ax.errorbar(x, y, yerr=yerr, errorevery=5)
+ax.set_title('only every 5th errorbar')
+
+
+fig.suptitle('Errorbar subsampling for better visualibility')
+
+plt.show()
diff --git a/lib/matplotlib/axes.py b/lib/matplotlib/axes.py
@@ -5159,7 +5159,8 @@ def errorbar(self, x, y, yerr=None, xerr=None,
             
           *errorevery*: positive integer
             subsamples the errorbars. Eg if everyerror=5, errorbars for every
-            5-th datapoint will be plotted.
+            5-th datapoint will be plotted. The data plot itself still shows
+            all data points.
 
         All other keyword arguments are passed on to the plot command for the
         markers. For example, this code makes big red squares with
@@ -5194,6 +5195,9 @@ def errorbar(self, x, y, yerr=None, xerr=None,
 
         """
 
+        if errorevery < 1:
+            raise ValueError('errorevery has to be a strictly positive integer ')
+
         self._process_unit_info(xdata=x, ydata=y, kwargs=kwargs)
         if not self._hold: self.cla()
         holdstate = self._hold
