Re: [matplotlib-devel] Passing errorbar width arguments to bar/barh ?

[John H. <jd...@gm...>]

On Tue, Jun 1, 2010 at 6:17 PM, Fernando Perez <fpe...@gm...> wrote:
> Hi all,
>
> I just spent some time digging through the matplotlib code, and I see
> that the errorbar line width argument isn't passed through to the
> underlying call.  In axis.bar, we have this code:
>
>        if xerr is not None or yerr is not None:
>            if orientation == 'vertical':
>                # using list comps rather than arrays to preserve unit info
>                x = [l+0.5*w for l, w in zip(left, width)]
>                y = [b+h for b,h in zip(bottom, height)]
>
>            elif orientation == 'horizontal':
>                # using list comps rather than arrays to preserve unit info
>                x = [l+w for l,w in zip(left, width)]
>                y = [b+0.5*h for b,h in zip(bottom, height)]
>
>            self.errorbar(
>                x, y,
>                yerr=yerr, xerr=xerr,
>                fmt=None, ecolor=ecolor, capsize=capsize)
>
> while errorbar has this signature:
>
>    def errorbar(self, x, y, yerr=None, xerr=None,
>                 fmt='-', ecolor=None, elinewidth=None, capsize=3,
>                 barsabove=False, lolims=False, uplims=False,
>                 xlolims=False, xuplims=False, **kwargs):
>
> For a poster, we wanted thicker errorbars drawn and had to resort to:
>
> plt.rcParams['lines.markeredgewidth'] = 2
> plt.rcParams['lines.linewidth'] = 2
>
> and reverting back to normal width after making the errorbar calls.
> Should I file a ticket about this, or are such fine-tuning tasks
> considered as fair game for rcParams manipulations?
>
> I'm happy to file the ticket, I just don't want to create unnecessary
> noise if the rcparams is meant to be 'the way' to do it.

While this is certainly a bug that needs to be fixed (and Eric is
right that these functions are heavily overworked and hairy), there is
a better workaround than the one you tried.  From the errorbar
docstring:



        Return value is a length 3 tuple.  The first element is the
        :class:`~matplotlib.lines.Line2D` instance for the *y* symbol
        lines.  The second element is a list of error bar cap lines,
        the third element is a list of
        :class:`~matplotlib.collections.LineCollection` instances for
        the horizontal and vertical error ranges.

So you can call the appropriate methods on the return objects.  Eg

  ylines, caplines, vlines = ax.errorbar(...)

if you want to set the vertical line thickness, it is a LineCollection
instance so you can call

  vlines.set_linewidth(2.0)

Since it is a Collection instance, you can also vary the vertical
linewidths by passing in a sequuence of linewidths.

Hope this helps,
JDH