Re: [PyX-devel] Re: [PyX-user] bar chart x-axis custom labels

[pieter c. <pi...@cl...>]

Andre,

I had a go at looking at your code, but without understanding the larger
implementation, I am lost. However, I am interested in this and will have
a go at it again later.

A few questions if I may (this might be answered earlier in the list, so
tell me to stop if that is the case):
1. How does pyx make use of TeX? What is the integration and purpose of
the integration?
2. What is the basic idea behind the library design? I can see from the
documentation the basic workflow, but what about the underlying principles
for the implementation?

As to labels and tics: This I think is a difficult subject because in many
libraries it is not an easy subject and the implementor requires a
significant amount of knowledge to do anything other than use defaults. To
make it more user friendly, I have the following suggestions (and will
help implement where I can)
1. To develop a number of use-cases and appropriate examples for manual
overried that include:
1.1. Example of no labels on all types graphs
1.2. Example of manual labels on all types of graphs
1.3. ...
2. Would it be possible to provide a manual override parameter to all axis
that allows users to provide a list of values or [[value,label],..] that
will then be converted to chart-coordinates and plotted at value location
on the axis? This would provide ultimate flexibility.

I have been thinking about a first set of requirements for the histogram
class and here is my stab at them.

REQUIRED
1. To plot steps like gnuplot.
2. To plot multiple series on a graph.
3. To provide manual overrides on the x-axis.
4. To cater for both continuous as well as discreet x-values (this again
is a little unclear but I can imagine that not all statistical sampling
would be agains continues values)

DESIRED
1. To provide the facility to swap axis (this I cannot justify, but can
imagine that it would be valuable.

http://en.wikipedia.org/wiki/Histogram

Pieter

> Hi Pieter,
>
> welcome on pyx-dev (which is kind of low traffic most of the time as
> pyx-user as well) ... ;-)
>
> On 02.02.05, pieter claassen wrote:
>> 1. Top plot this data so that it can be seen that there were 55 trips
>> that
>> took 95 minutes and 45 minutes that took 100 minutes.
>> 2. To show that the distribution of the results are mostly on the high
>> end.
>>
>> To recap the current problem:
>> When this large number of data points are plotted on a bar graph, the
>> x-axis labels overwrite each other.
>>
>> Current suggested solution:
>> ??
>
> Well, not really. As I said before, you should try to use a x-y-plot
> for that. A bar graph is just the wrong thing for that.
>
>> Any suggestions on how to proceed?
>
> You'll need a histogram style. There are basically two ways to get it.
> You could create a style from graph.style.linestyle, overwrite the
> drawpoint method and call the graph.style.linestyle's drawpoint
> several times for each point with appropriately modified
> sharedata.vposi data to get the step-like shape. The other possibility
> would be to write your own style from scratch. A simple, first working
> example could look like:
>
>     import random
>     from pyx import *
>
>     class histogram(graph.style._styleneedingpointpos):
>
>         needsdata = ["vpos", "vposmissing", "vposavailable"]
>
>         defaultlineattrs = []
>
>         def __init__(self, lineattrs=[]):
>             self.lineattrs = lineattrs
>
>         def selectstyle(self, privatedata, sharedata, graph, selectindex,
> selecttotal):
>             if self.lineattrs is not None:
>                 privatedata.lineattrs =
> attr.selectattrs(self.defaultlineattrs + self.lineattrs,
> selectindex, selecttotal)
>             else:
>                 privatedata.lineattrs = None
>
>         def initdrawpoints(self, privatedata, sharedata, graph):
>             privatedata.path = path.path()
>             privatedata.lastvpos = None
>
>         def drawpoint(self, privatedata, sharedata, graph):
>             if sharedata.vposavailable:
>                 if privatedata.lastvpos:
>                     midvxpos = 0.5 * (privatedata.lastvpos[0] +
> sharedata.vpos[0])
>                     privatedata.path.append(path.lineto_pt(*graph.vpos_pt(midvxpos,
> privatedata.lastvpos[1])))
>                     privatedata.path.append(path.lineto_pt(*graph.vpos_pt(midvxpos,
> 0)))
>                     privatedata.path.append(path.lineto_pt(*graph.vpos_pt(midvxpos,
> sharedata.vpos[1])))
>                     privatedata.path.append(path.lineto_pt(*graph.vpos_pt(*sharedata.vpos)))
>                 else:
>                     privatedata.path.append(path.moveto_pt(*graph.vpos_pt(*sharedata.vpos)))
>                 privatedata.lastvpos = sharedata.vpos[:]
>             else:
>                 privatedata.lastvpos = None
>
>         def donedrawpoints(self, privatedata, sharedata, graph):
>             if privatedata.lineattrs is not None and
> len(privatedata.path.path):
>                 graph.stroke(privatedata.path, privatedata.lineattrs)
>
>
>     g = graph.graphxy(width=8)
>     g.plot(graph.data.list([(5*i, random.random()) for i in range(1, 20)],
> x=1, y=2), [histogram()])
>     g.writeEPSfile("histogram")
>
>
> However, its just a starting point. We do not correctly adjust the
> vertical range. We do not know how to handle the edge points
> (currently particial boxes are plotted --- we could, of course, just
> plot steps (like gnuplot and others, but I'm not sure whether this is
> a good idea)). We do not cut the path at the graph border. We can't
> exchange x and y axis ... etc.
>
> Any comments how to proceed? What's needed out there? (I do not need
> histograms at all, otherwise I would have implemented such a style
> before already, but since we're now on the subject, we might get it
> done once and for all ...) Although its working well that way, its not
> that easy to make it a robust graph style. As usual with graph styles.
> Its easy to implement one, but to make it general perpose, some more
> work needs to be done ...
>
>
> André
>
> --
> by  _ _      _    Dr. André Wobst
>    / \ \    / )   wo...@us..., http://www.wobsta.de/
>   / _ \ \/\/ /    PyX - High quality PostScript figures with Python & TeX
>  (_/ \_)_/\_/           visit http://pyx.sourceforge.net/
>
>
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