matplotlib-users

[Matplotlib-users] errorbar with one value + scatter

[Arnold M. <arn...@wu...>]

Dear all,

Praise for this first serious python plotting package!

I have two minor comments:

-> when I try to do an errorbar plot with a scalar, rather than an array 
as the argument (i.e. errorbar(scalar_x, scalar_y, xerr=scalar_xerr)) I 
get the following error message:

"/usr/lib/python2.3/site-packages/matplotlib/axes.py", line 569, in errorbar
     right = x+xerr[1]
IndexError: index out of bounds

This is due to the fact that the length of xerr is tested only to be 1 
or greater than 1 (asymmetric errors). However, the option that I would 
like to plot just one point is not included. So an extra if-clause is 
needed before the present code that checks whether x and xerr are arrays 
or not.

-> I very much like the option for scatter to color the blobs to be 
plotted. However, I have an application where the shape of the blobs is 
immaterial: I would rather have filled circles (or even better: filled 
symbols, be it circles, triangles ...). Anyhow: I would like them to be 
symmetric irrespective of the range of the axes. One option would be to 
allow the s-keyword to be allowed to be negative, where negative means: 
symmetric and the value of the negative number being the size relative 
to some default size.

Thanks and keep up the good work,

Arnold Moene

Re: [Matplotlib-users] errorbar with one value + scatter

[John H. <jdh...@ac...>]

>>>>> "Arnold" == Arnold Moene <arn...@wu...> writes:

    Arnold> Dear all, Praise for this first serious python plotting
    Arnold> package!

Thanks!

    Arnold> I have two minor comments:

    -> when I try to do an errorbar plot with a scalar, rather than an
    Arnold> array as the argument (i.e. errorbar(scalar_x, scalar_y,
    Arnold> xerr=scalar_xerr)) I get the following error message:

    Arnold> "/usr/lib/python2.3/site-packages/matplotlib/axes.py",
    Arnold> line 569, in errorbar right = x+xerr[1] IndexError: index
    Arnold> out of bounds

    Arnold> This is due to the fact that the length of xerr is tested
    Arnold> only to be 1 or greater than 1 (asymmetric
    Arnold> errors). However, the option that I would like to plot
    Arnold> just one point is not included. So an extra if-clause is
    Arnold> needed before the present code that checks whether x and
    Arnold> xerr are arrays or not.

Well, the behavior you are seeing is the correct, documented behavior.
I think it would be easier for you to pass errorbar what it is
expecting than for errorbar to handle this additional use case - it's
already getting pretty hairy in there.

DO you have a problem doing

  errorbar([1],[2],xerr=[.1])


    -> I very much like the option for scatter to color the blobs to
    -> be
    Arnold> plotted. However, I have an application where the shape of
    Arnold> the blobs is immaterial: I would rather have filled
    Arnold> circles (or even better: filled symbols, be it circles,
    Arnold> triangles ...). Anyhow: I would like them to be symmetric
    Arnold> irrespective of the range of the axes. One option would be
    Arnold> to allow the s-keyword to be allowed to be negative, where
    Arnold> negative means: symmetric and the value of the negative
    Arnold> number being the size relative to some default size.

You're not the first!  The temporary workaround is to use
plot(x,y,'o') which uses fixes sizes in points for the symbols (you
can also use '*', '+', etc)  However, you cannot vary the size or
color of the symbols so this may not be workable.  

When I refactor the scatter / pcolor etc commands as discussed in my
response to Dominique Orban above, I'll make sure that this case is
handled as well.  I plan to support efficient handling of scatter with
arbitrary (or at least several) shapes where the size can be in data
(x,y) or user-defined coords, eg, physical sizes.  It would be helpful
for me if people gave some information about how they would like
scatter to behave, particularly in regard to the sizes since I am
still working this out.  

Would you like physical sizes, eg circles with radius in points, or
what?

Should the shape depend on the aspect ratio of the plotting window.
Eg, if it's a circle and you have a short, wide window, should it
appear ellipsoidal?

What basic scatter symbols should be supported?

What are the most common uses: fixed size?  fixed color?  vary both?

JDH