ylabels for secondary_y axis

modified Selective Plotting on Secondary Y-axis example to show how to set ylabels for both left and right y axis

Author: adamgreenhall

doc/source/visualization.rst

@@ -129,9 +129,12 @@ keyword:
 .. ipython:: python
 
    plt.figure()
+   ax = df.plot(secondary_y=['A', 'B'])
+   ax.set_ylabel('CD scale')
+   @savefig frame_plot_secondary_y.png width=4.5in   
+   ax.right_ax.set_ylabel('AB scale')
+
 
-   @savefig frame_plot_secondary_y.png width=4.5in
-   df.plot(secondary_y=['A', 'B'])
 
 Note that the columns plotted on the secondary y-axis is automatically marked
 with "(right)" in the legend. To turn off the automatic marking, use the
@@ -141,7 +144,7 @@ with "(right)" in the legend. To turn off the automatic marking, use the
 
    plt.figure()
 
-   @savefig frame_plot_secondary_y.png width=4.5in
+   @savefig frame_plot_secondary_y_no_right.png width=4.5in
    df.plot(secondary_y=['A', 'B'], mark_right=False)