Re: [Matplotlib-users] Update values of errorbars [solved]

[G. D. <g....@in...>]

On 11/16/2010 07:41 PM, Stan West wrote:
> I believe I see how you could do it.  The errorbar call returns the tuple p =
> (plotline, caplines, barlinecols) [1], and to update the errorbars, you must
> modify the objects in the caplines and barlinecols lists.  Each element of the
> caplines list is a Line2D artist [2] for the left, right, top, or bottom caps;
> you can use its methods set_data, set_xdata, or set_ydata to modify its
> coordinates, as you did for the main line.  Each element of the barlinecols
> list is a LineCollection [3] artist responsible for all of the x or y
> errorbars; you can use the set_segments method to provide new coordinates.
>
> [1]
> http://matplotlib.sourceforge.net/api/axes_api.html#matplotlib.axes.Axes.errorbar
> [2]
> http://matplotlib.sourceforge.net/api/artist_api.html#matplotlib.lines.Line2D
> [3]
> http://matplotlib.sourceforge.net/api/collections_api.html#matplotlib.collections.LineCollection
>    
Thanks Stan,
with your suggestion I was able to solve the problem, even if it is not 
immediate (but not too long). This is what I did:

plotline, caplines, barlinecols = plt.errorbar(x, y, yerr, xerr)

# Now move the line
y = y/2.

# Replot the data first
plotline.set_data(x,y)

# Find the ending points of the errorbars
error_positions = (x-xerr,y), (x+xerr,y), (x,y-yerr), (x,y+yerr)

# Update the caplines
for i,pos in enumerate(error_positions):
     caplines[i].set_data(pos)

# Update the error bars
barlinecols[0].set_segments(zip(zip(x-xerr,y), zip(x+xerr,y)))
barlinecols[1].set_segments(zip(zip(x,y-yerr), zip(x,y+yerr)))

The last lines are a little clumsy, but I could not find a better way. 
Anyway, it could be nice to have a method like set_errorbar(x, y, yerr, 
xerr) to do the job.

Many thanks again

Gianfranco
-- 

Istituto Nazionale di Ricerca Metrologica (I.N.Ri.M)
(former Istituto Elettrotecnico Nazionale Galileo Ferraris)
Strada delle Cacce, 91 - 10135 Torino Italy
tel: ++39 011 3919839    fax: ++39 011 3919834
Personal home page: http://www.inrim.it/~durin/
INRiM home pag: http://www.inrim.it/
=============================================================
Please note my new e-mail: g....@in...
=============================================================