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## matplotlib-users

 [Matplotlib-users] Update values of errorbars From: Gianfranco Durin - 2010-11-10 16:50:11 ```Dear mpl users, I have the following problem to solve. Imagine to have the simple example reported on website plotting the errorbars of some x,y data: #!/usr/bin/env python import numpy as np import matplotlib.pyplot as plt # example data x = np.arange(0.1, 4, 0.5) y = np.exp(-x) # example variable error bar values yerr = 0.1 + 0.2*np.sqrt(x) xerr = 0.1 + yerr # First illustrate basic pyplot interface, using defaults where possible. plt.figure() plt.errorbar(x, y, xerr=0.2, yerr=0.4) ================================================ Now I change the last line into: p = plt.errorbar(x, y, xerr=0.2, yerr=0.4) and if I change, for instance, y: y = y/2. I can easily replace the x,y with: p[0].set_data(x,y) but I do not know how to do the same for the errorbars. I need to do this as I am implementing a code with a GUI written in PyQt4, and I need to quickly replot some data. Can anyone help me? Many thanks in advance Gianfranco Durin ```
 Re: [Matplotlib-users] Update values of errorbars From: Stan West - 2010-11-16 18:43:41 ```> From: Gianfranco Durin [mailto:g.durin@...] > Sent: Wednesday, November 10, 2010 11:32 > > Dear mpl users, > I have the following problem to solve. Imagine to have the > simple example reported on website plotting the errorbars of > some x,y data: ... > and if I change, for instance, y: > > y = y/2. > > I can easily replace the x,y with: > > p[0].set_data(x,y) > > but I do not know how to do the same for the errorbars. 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.error bar [2] http://matplotlib.sourceforge.net/api/artist_api.html#matplotlib.lines.Line2D [3] http://matplotlib.sourceforge.net/api/collections_api.html#matplotlib.collecti ons.LineCollection ```
 Re: [Matplotlib-users] Update values of errorbars [solved] From: G. Durin - 2010-11-23 13:34:27 ```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.durin@... ============================================================= ```
 Re: [Matplotlib-users] Update values of errorbars [solved] From: Stan West - 2010-12-03 19:28:53 ```> From: G. Durin [mailto:g.durin@...] > Sent: Tuesday, November 23, 2010 08:34 > # 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. I'm glad you were able to solve your problem. An alternative to the above lines is barlinecols[0].set_segments( np.array([[x - xerr, y], [x + xerr, y]]).transpose((2, 0, 1)) ) and likewise for y. The transposition produces a depth stack of 2-by-2 arrays. ```