set legend for plot with several lines (in python)

Question

I have several lines plotted in the same figure and I want name this group of lines according to its content. Over those lines I intended yet to plot the average with the errorbar. But two main problem arise:

1) My legend does not appear as I intend (even trying to plot a extra point out of the range of the figure I can't give them a name - workaround)

2) the plot with the average and errorbars is not superposed. Sometimes it is in front and sometimes it is behind the other curves.

What should I do to get it fixed? I could do it in Matlab (same problem for Matlab) But did not find the answer for python.

This is the part of the plot of my routine:

    UYavg = np.nanmean(UYbvall,0)
    yerr = np.nanstd(UYbvall,0)
    plt.figure()
    for i in range(71):
        plt.plot(LTbvall[i],UYbvall[i],'r-')
    l1 = plt.plot([-2,-1],[1,2],'r-')
    l2 = plt.plot(LTbvall[3],UYavg,'b*-')
    plt.errorbar(LTbvall[2],UYavg, yerr = yerr,ecolor='b')
    plt.xlabel('Tempo (LT)')
    plt.xlim(0,24)
    plt.ylabel('Uy (m/s)')
    plt.title('Vento neutro zonal calculado pelo modelo NWM (BV)')
    plt.legend((l1,l2),('Perfis COPEX','Media'), loc = 'best')

EDIT: the answer must be similar to Multiple lines in a plot or make-custom-legend-in-matplotlib

I think you'll need to produce a [Minimal, Complete, Verifiable Example](http://stackoverflow.com/help/mcve). Based on your current code, with the comment I made below --- it should be working. — DilithiumMatrix, Oct 25 '15 at 21:48
I posted below an answer that solves problem 1. It did not work with the comments so far. — Claudia, Oct 25 '15 at 23:47

score 24 · Answer 1 · answered Oct 24 '15 at 21:07

24

I find the easiest solution is to give the lines labels at creation. Try the following, you will see both lines show up on the legend:

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], color='red', label='line one')
plt.plot([4, 6, 8], color='blue', label='line two')
plt.legend()
plt.show()

answered Oct 24 '15 at 21:07

BlivetWidget

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@BivetWidget: yes name it at creation is the best way but in my case I would have 71curves with the same name and no spece for the legend at all. Instead I intended to name the group of lines with a single name and add the label of the other curves after – Claudia Oct 25 '15 at 19:48
@Claudia I believe that if you give them all the same label, they'll just show up as one item in the legend, which I think is what you want. On a camping trip now, so I can't test that assertion at the moment though. – BlivetWidget Oct 26 '15 at 03:26
I tested it, and unless you define which should appear all of them come out. – Claudia Oct 26 '15 at 10:57
@Claudia I'm back in town now, and I guess not. I suppose if I were just trying to label a group of lines (not something I generally need to do), then I would only give the first plot a label. Would be trivial since you can test for where you are in the loop of plot creation. – BlivetWidget Oct 27 '15 at 23:26

score 10 · Accepted Answer · edited May 23 '17 at 11:45

Well based on another questions (make-custom-legend-in-matplotlib and force-errorbars-to-render-last-with-matplotlib) I got it right. The second error should not happen, I think there may be a bug on zorder option. If I select only the larger number for the error bar, the plot of error bar continues hiden. So I had to set a negative number for the zorder for the lines in the for loop.

The lines that fix the problems are:

fig = plt.figure()
ax = fig.add_subplot(1,1,1)
for i in range(71):
    ax.plot(LTbvall[i],UXbvall[i],'-',color ='#C0C0C0',label = 'Perfis COPEX',zorder = -32)
ax.plot(LTbvall[3],UXavg,'b*-', label = u'média')
ax.errorbar(LTbvall[3],UXavg, yerr = yerr,ecolor='b',zorder = 10)
#Get artists and labels for legend and chose which ones to display
handles, labels = ax.get_legend_handles_labels()
display = (0,71)
ax.set_xlabel('Tempo (LT)')
ax.set_xlim(0,24)
ax.set_ylabel('Ux (m/s)')
ax.set_title('Vento neutro meridional calculado pelo modelo NWM (BV)')
ax.legend([handle for i,handle in enumerate(handles) if i in display],
      [label for i,label in enumerate(labels) if i in display], loc = 'best')
fig.savefig(path[9] + 'Uxbvall_LT_nwm')
plt.clf() 
plt.gcf()
plt.close()

The output is as follows:

score 1 · Answer 3 · answered Oct 25 '15 at 20:42

1

I'm surprised you're not getting an error message when you try to create your legend. The plt.plot command always returns a tuple, so you should be catching l1, = plt.plot(...). Does that fix it?

answered Oct 25 '15 at 20:42

DilithiumMatrix

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set legend for plot with several lines (in python)

3 Answers3