Matplotlib Legends not working
PythonPlotMatplotlibPython Problem Overview
Ever since upgrading matplotlib I get the following error whenever trying to create a legend:
/usr/lib/pymodules/python2.7/matplotlib/legend.py:610: UserWarning: Legend does not support [<matplotlib.lines.Line2D object at 0x3a30810>]
Use proxy artist instead.
http://matplotlib.sourceforge.net/users/legend_guide.html#using-proxy-artist
warnings.warn("Legend does not support %s\nUse proxy artist instead.\n\nhttp://matplotlib.sourceforge.net/users/legend_guide.html#using-proxy-artist\n" % (str(orig_handle),))
/usr/lib/pymodules/python2.7/matplotlib/legend.py:610: UserWarning: Legend does not support [<matplotlib.lines.Line2D object at 0x3a30990>]
Use proxy artist instead.
http://matplotlib.sourceforge.net/users/legend_guide.html#using-proxy-artist
warnings.warn("Legend does not support %s\nUse proxy artist instead.\n\nhttp://matplotlib.sourceforge.net/users/legend_guide.html#using-proxy-artist\n" % (str(orig_handle),))
This even occurs with a trivial script like this:
import matplotlib.pyplot as plt
a = [1,2,3]
b = [4,5,6]
c = [7,8,9]
plot1 = plt.plot(a,b)
plot2 = plt.plot(a,c)
plt.legend([plot1,plot2],["plot 1", "plot 2"])
plt.show()
I've found the link that the error points me towards pretty useless in diagnosing the source of the error.
Python Solutions
Solution 1 - Python
You should add commas:
plot1, = plt.plot(a,b)
plot2, = plt.plot(a,c)
The reason you need the commas is because plt.plot() returns a tuple of line objects, no matter how many are actually created from the command. Without the comma, "plot1" and "plot2" are tuples instead of line objects, making the later call to plt.legend() fail.
The comma implicitly unpacks the results so that instead of a tuple, "plot1" and "plot2" automatically become the first objects within the tuple, i.e. the line objects you actually want.
http://matplotlib.sourceforge.net/users/legend_guide.html#adjusting-the-order-of-legend-items
https://stackoverflow.com/questions/10422504/line-plotx-sinx-what-does-comma-stand-for?rq=1
Solution 2 - Python
Use the "label" keyword, like so:
plt.plot(x, y, label='x vs. y')
and then add the legend like so:
plt.legend()
The legend will retain line properties like thickness, colours, etc.
Solution 3 - Python
Use handles
AKA Proxy artists
import matplotlib.lines as mlines
import matplotlib.pyplot as plt
# defining legend style and data
blue_line = mlines.Line2D([], [], color='blue', label='My Label')
reds_line = mlines.Line2D([], [], color='red', label='My Othes')
plt.legend(handles=[blue_line, reds_line])
plt.show()
Solution 4 - Python
use label while plotting graph then only u can use legend. x axis name and y axis name is different than legend name.