Re: [Matplotlib-users] barchart errorbars always in both directions

[Benjamin R. <ben...@ou...>]

On Wed, May 23, 2012 at 4:03 AM, Meesters, Aesku.Kipp Institute <
mee...@ae...> wrote:

> Hi,
>
> I'm following the example in the gallery to do a barchart plot (see
> http://matplotlib.sourceforge.net/examples/api/barchart_demo.html ).
>
> In contrast to the example I would like to see the error bars only above
> the bars, so I tried
>
> rects2 = ax.bar(ind+width, womenMeans, width, color='y',
>                yerr=stds, error_kw = {'barsabove': True,
>                                       'ecolor'   : 'k'}
>
> While the 'ecolor' argument gets accepted, 'barsabove' apparently has no
> effect (error bars still point up and downwards) - yet, no warning /
> error is triggered. Where is my mistake? Or is this a bug (still using
> version 1.0.1) with a known work-around?
>
> TIA
> Chris
>
>
Chris,

I don't think "barsabove" does what you want.  By "above", it means that
the errorbar is plotted in a layer on top of the plotting symbol rather
than in the layer under it.  Both ends will be plotted.

To get what you want, you might want to try (Note: untested):

rects2 = ax.bar(ind+width, womenMeans, width, color='y',
               yerr=np.vstack([[0]*len(stds), stds]), error_kw = {'ecolor'
  : 'k'})

When yerr is a 2xN numpy array, errorbars are plotted at y-yerr[0, :] and
y+yerr[1,:]. So, np.vstack creates a 2xN array where the first row is all
zeros and the second row is the stds values.

I hope that works for you!
Ben Root