On Tue, Dec 16, 2008 at 10:09 AM, Michael Oevermann
<michael.oeverm...@tu-berlin.de> wrote:
> Hi all,
>
> I am trying to find a solution to the following problem (without
> success so far):
> I have some high frequency data which I want to plot with a simple
> plot command using a solid line and a symbol. However, since I have many
> many
> data points I want to plot the symbol only every N'th data point. Is
> there a skip parameter
> or any other way to tell matplotlib to actually plot the symbol only
> at every N'th data point (I know it is possible in grace which I have
> stopped
> using in favour of matplotlib). Plotting the data twice- the first time
> without
> symbol showing every data point and the second time onlywith the symbol
> and some skip in the data - doesn't help as I now get two entities in
> the legend.
There is a way to do this, but it is not terribly elegant. The tricky
part is to get the legend right::
import numpy as np
import matplotlib.pyplot as plt
fig = plt.figure()
ax = fig.add_subplot(111)
N = 10
x = np.arange(100.)
y = x**2
# the solid line, suppress auto legend
line1, = ax.plot(x, y, linestyle='-', color='black', label='_nolegend_')
# every N-th marker, suppress auto legend
line2, = ax.plot(x[::N], y[::N], linestyle='', marker='o',
markerfacecolor='blue', label='_nolegend_')
# the proxy line, both solid and markers. Don't add it to plot, just
# use it in legend
import matplotlib.lines as lines
proxyline = lines.Line2D([0,1], [0,1], linestyle='-',
color='black', marker='o', markerfacecolor='blue')
leg = ax.legend([proxyline], ['my label'])
plt.show()
JDH
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