[Pyx-user] Re: bars with errors

[Marko V. <ma...@io...>]

Thanks, the bug is fixed, indeed :).

> For 0.7 I'm working to allow several styles within one plot command.
> I want to allow errorbars at bar graphs without further thoughts:
>
> g.plot(graph.data.list(xname=1, y=2, dy=3), [graph.style.bar(), graph.style.errorbar()])

I guess it should be

g.plot(graph.data.list(xname=1, y=2, dy=3), [graph.style.bar(), graph.style.symbol()]) ?


> I also want to enable insertion of text at the top (or another
> position) of a bar graph and others. Another gain will be an easier
> extention of existing styles without copying much code as it currently
> can be, because graph styles are still quite monolithic. So you have
> to wait for another two or three months. (Beside that I could explain
> you the bar dist etc. when you ask questions about it ...)

Excellent plan! OK, I'll ask about positioning of the bars (to draw bars
with errors during 2-3 month).

It seems that, in the simplest case, centers of the bars are at positions
1, 2, 3, ... and the limits of the axis are min=0.5 to max=N+0.5 (N is the
number of bars).

Situation is somewhat more difficult if there are multiple bars per each
category (as in the second plot of examples/bar.py). For example, if we
have NSubCols in each of the groups of bars, then the center of each of
the subbars is at

	x = j + 1 + (i - NSubCols/2.0 + 0.5)*w

where j is index of the group (from 0 to N-1), i is the index of the
subbar, and w is the width of the subbar. The width of the subbar is
determined by NSubCols and argument dist given to axis.bar() as follows:

	w = 1.0 / (NSubCols + dist)

However, these formula work only in the case if dist for multisubaxis is
set equal to zero. How should I modify these formula to get them work on
general case (with the both dist given for axis and multisubaxis)?

Best wishes,

Marko