Re: [Pyx-user] help regarding the plot

[Andre W. <wo...@us...>]

Hi,

On 21.01.04, Michael Schindler wrote:
> ######## python code ###########################
> # read x, y values from your datafile
> d = data.datafile("minimal.dat")
> 
> # extract the x and y values separately
> xvals = d.getcolumn(1)
> yvals = d.getcolumn(2)
> 
> # plot the top line of your data with a line
> # (or with symbols, if you like)
> g = graph(width=8)
> g.plot(graph.data(d, x=1, y=2), style=graph.line())
> 
> # finish the graph so that all axes are fixed
> g.finish()
> 
> # now comes the workaround: you can draw lines on the graph-canvas
> # directly. Use g.pos() for accessing the data-coordinate system:
> for x,y in zip(xvals,yvals):
>   g.stroke(path.line(g.pos(x,y)[0], g.pos(x,y)[1],
>                      g.pos(x,0)[0], g.pos(x,0)[1]))
> 
> g.writetofile("minimal")
> ################################################

Some additional notes:

1) You even may want to skip the g.plot(...) completely. Then the
   graph will not know about the axis ranges, so you have to provide
   axes with fixed ranges in the graph constructor. This would look
   like:

     g = graph.graphxy(width=8,
                       x=graph.linaxis(min=0, max=10),
                       y=graph.linaxis(min=0, max=10))

2) When you want to plot data, you already have within python lists,
   you can construct a data instance yourself to use them in plot
   methods of the graph. An example would be:

     d = data.data([[1, 1], [2, 4], [3, 9], [4, 16], [5, 25]])

   The valid column numbers are 0 and 1 for this case. Note that when
   reading a dataset from a file the columns are numbered from 1,
   while the column 0 is added automatically and contains the line
   number.

3) It is possible to create own data styles to be used in the graph.
   While this is not yet well documented, you have to look into the
   graph sources for that. I should note, that the graph styles are
   subject of a complete redesign and documentation in the forthcoming
   releases.


André

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