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Dear Paul,

Thank you, it does exacly what I want to do. I searched a bit into the
"contour" instance, but I was biased since I was looking for something
like "get_line".

cheers

Francesco


2011/1/21 Paul Ivanov <piv...@gm...>:
> Francesco Montesano, on 2011-01-21 15:44,  wrote:
>> Dear All,
>>
>> I am using contour plot and I am drawing different contours with
>> different colors and linestyles and I would like to have a legend with
>> a caption for each contour function used.
>> Here you can see an example of what I would like to do
>>
>> >> #create the 2D histogram and the x and y axis
>> >> x, y = np.random.normal(0, 0.5, 1000), np.random.normal(0, 1, 1000)
>> >> h, xe,ye = np.histogram2d(x,y, bins=25)
>> >> xe, ye = (xe[1:]+xe[:-1])/2, (ye[1:]+ye[:-1])/2
>> >>
>> >> lines,text = [], []   # initialise lists
>> >>
>> >> #contour plots
>> >> lines.append(plt.contour(xe,ye,h, levels=[10,9], linestyles="-", colors="k"))
>> >> text.append("level=10, 9")
>> >>
>> >> lines.append(plt.contour(xe,ye,h, levels=[5,4], linestyles="--", colors="r"))
>> >> text.append("level=5, 4")
>> >>
>> >> plt.legend(lines, text)
>>
>> Everything goes well untill I plot the legend. At the end of the mail
>> I report the error that I get.
>> Anyway, if I do
>> >> plt.legend(lines)
>> I don't get any errors but it's quite useless, since the text of the
>> legend is just like:
>> <matplotlib.contour.ContourSet instance at 0x6bedc20>
>> as you can see from the attached figure.
>>
>>
>> I've the feeling that the problem is that "contour" gives back a
>> "matplotlib.contour.ContourSet instance", while the functions like
>> "plot" gives back a "<matplotlib.lines.Line2D object".
>>
>> Does anyone knows how to do what I want?
>>
> Hi Francesco,
>
> here's one way of getting what you want, instead of calling
> legend on your 'lines' variable as you had it, do this:
>
>  actual_lines = [cs.collections[0] for cs in lines]
>  plt.legend(actual_lines, text)
>
> As you note, the call to plt.countour does not return lines, it
> returns contour sets (which is why I called the variable 'cs' in
> my example). Poking around in ipython, I saw that each contour
> set has a collections attribute which holds the actual lines.
>
> hope that helps,
> --
> Paul Ivanov
> 314 address only used for lists,  off-list direct email at:
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