matplotlib-users Mailing List for matplotlib

To compare two histograms you can plot a bihistogram as suggested on
http://www.itl.nist.gov/div898/handbook/eda/section3/bihistog.htm

The little function I've written to do so is below. See if it helps.

Antonio



import scipy
from pylab import figure

def bihist(y1, y2, nbins=10, h=None):
	'''
	Bihistogram.
	h is an axis handle. If not present, a new figure is created.
	'''
	if h is None: h = figure().add_subplot(111)
	xmin = scipy.floor(scipy.minimum(y1.min(), y2.min()))
	xmax = scipy.ceil(scipy.maximum(y1.max(), y2.max()))
	bins = scipy.linspace(xmin, xmax, nbins)
	n1, bins1, patch1 = h.hist(y1, bins)
	n2, bins2, patch2 = h.hist(y2, bins)
	# set ymax:
	ymax = 0
	for i in patch1:
		height = i.get_height()
		if height > ymax: ymax = height
	# invert second histogram and set ymin:
	ymin = 0
	for i in patch2:
		height = i.get_height()
		height = -height
		i.set_height(height)
		if height < ymin: ymin = height
	h.set_ylim(ymin*1.1, ymax*1.1)		
	h.figure.canvas.draw()

Luca,

It is a bug that appears when recent mpl is used with Numeric as opposed 
to numpy or numarray.  It is fixed in svn.  Your possible solutions are:

1) Use numpy or numarray instead of Numeric
2) Build mpl from svn
3) Edit axes.py as indicated in this diff chunk:

@@ -1217,7 +1217,7 @@
          ACCEPTS: len(2) sequence of floats
          """

-        if xmax is None and hasattr(xmin,'__len__'):
+        if xmax is None and iterable(xmin):
              xmin,xmax = xmin

          old_xmin,old_xmax = self.get_xlim()
@@ -1330,7 +1330,7 @@
          ACCEPTS: len(2) sequence of floats
          """

-        if ymax is None and hasattr(ymin,'__len__'):
+        if ymax is None and iterable(ymin):
              ymin,ymax = ymin

          old_ymin,old_ymax = self.get_ylim()


Eric

luc...@li... wrote:
> Hello I have installed matplotlib on su 10.0 
> 
> when i do only this example 
> 
> from pylab import *
> plot([1,2,3])
> 
> i get this error:
> only length-1 attays can be converted to Python scalars.
> 
> How i have made wrong?
> 
> Regards
> 
> Luca
> 
> 
> 
> 
> ------------------------------------------------------
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> 
> 
> 
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Hi folks,

I'm interested in hearing some strategies for plotting two histograms on 
the same plot.  My goal is
to visualize and compare two distributions which have similar shapes.

My first attempt was to use alpha, but this isn't well support on PS2 
output driver (surprising)
and I will be including these in a paper, so having a good print output 
format like PS2 or PDF is desired.
PDF seems to work ok, but the alpha model doesn't completely satisfy my 
in areas where the two
plots overlap a good deal.

import pylab, random

d1 = [random.gauss(0, 1) for i in range(100)]
d2 = [random.gauss(1, 1) for i in range(100)]

color = ['r', 'g']
pylab.hist(d1, facecolor='r', edgecolor='black', alpha=0.75)
pylab.hist(d2, facecolor='b', edgecolor='black', alpha=0.75)
pylab.savefig('test.pdf')
pylab.show()




What ideas do other people have?  My thought was to subdivide the plot 
into two subplots, and
plot one distribution on top, and the other on the bottom, but this 
effectively halves my vertical resolution
(I'm already plotting 24 subplots per page).

Thanks,
Dave

Try opening a python shell and type:

from pylab import *
a = [1,2,3]
a

What is a? Is it an array? Make sure you create an array by giving a
command like this:

a = array([1,2,3])

luc...@li... schreef:
> Hello I have installed matplotlib on su 10.0 
>
> when i do only this example 
>
> from pylab import *
> plot([1,2,3])
>
> i get this error:
> only length-1 attays can be converted to Python scalars.
>
> How i have made wrong?
>
> Regards
>
> Luca
>
>
>
>
> ------------------------------------------------------
> Mutui a tassi scontati da 40 banche. Richiedi online e risparmia...Servizio gratuito. www.mutuionline.it
> http://click.libero.it/mutuionline13nov
>
>
>
> -------------------------------------------------------------------------
> Using Tomcat but need to do more? Need to support web services, security?
> Get stuff done quickly with pre-integrated technology to make your job easier
> Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo
> http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642
> _______________________________________________
> Matplotlib-users mailing list
> Mat...@li...
> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
>
>   

>>>>> "Marek" =3D=3D Marek Szczypi=E4ski <Mar...@as...=
un.pl> writes:

    Marek> Hello All, I've been using matplotlib for some time now,
    Marek> and I want to connect it with zope. I'am using the example
    Marek> code from page:
    Marek> http://www.scipy.org/Cookbook/Matplotlib/Matplotlib_and_Zope
    Marek> , but whenever I try to import matplotlib, and/or pylab
    Marek> packages i get this error from zope:

    Marek> Error Type: RuntimeError Error Value: '/' is not a writable
    Marek> dir; you must set environment variable HOME to be a
    Marek> writable dir

    Marek> Have You got any ideas, on what might go wrong? I'am using
    Marek> matplotlib 0.87.4, and zope 2.9.5 with python 2.4.3 on
    Marek> gentoo linux box.

Have you tried following the advice in the error message=20

  "you must set environment variable HOME to be a writable dir"

>>>>> "lucaberto@libero" == lucaberto@libero it <luc...@li...> writes:

    lucaberto@libero> Hello I have installed matplotlib on su 10.0
    lucaberto@libero> when i do only this example

    lucaberto@libero> from pylab import * plot([1,2,3])

    lucaberto@libero> i get this error: only length-1 attays can be
    lucaberto@libero> converted to Python scalars.

    lucaberto@libero> How i have made wrong?

Please create a free-standing script

  from pylab import *
  plot([1,2,3])
  show()

and run it from the shell with

  > python test.py --verbose-helpful

and post the complete output back here.

JDH

Hello I have installed matplotlib on su 10.0 

when i do only this example 

from pylab import *
plot([1,2,3])

i get this error:
only length-1 attays can be converted to Python scalars.

How i have made wrong?

Regards

Luca

=0A=0A=0A------------------------------------------------------=0AMutui a=
 tassi scontati da 40 banche. Richiedi online e risparmia...Servizio grat=
uito. www.mutuionline.it=0Ahttp://click.libero.it/mutuionline13nov=0A

>>>>> "Eric" == Eric Firing <ef...@ha...> writes:

    Eric> Some discussion (and/or a ruling by John) is needed.  My
    Eric> preference is that if a change is made, it be a change in
    Eric> basic default behavior, not additional options, because any
    Eric> non-default behavior can be achieved easily using the extent
    Eric> kwarg in its present form, and at some point adding options
    Eric> and more complicated handling of kwargs causes more trouble
    Eric> (complex code and documentation) than it is worth.  I don't
    Eric> see any advantage of the present behavior over the
    Eric> matlab-equivalent behavior--but that may be because I am
    Eric> ignorant of the original rationale.

I'm weakly inclined to leave things as they are, since it is so easy
to get the desired behavior by setting the extent kwarg.  If we just
put a help string in the imshow docstring telling people how to get
what they want, that may suffice.  That said, I am a light user of
images and do not feel strongly at all.  If people who are heavy image
users feel strongly, I'm happy to change.  Perry?

    Eric> If imshow behavior is changed, a corresponding change will
    Eric> be needed in the image-matching capability of contour.
    Eric> Maybe matshow would also change; I haven't checked.

matshow doesn't really have much of a purpose any more.  It's primary
reason for being was to handle aspect ratio when aspect ratio was
broken.  Fernando -- do you see any reason to keep matshow?

JDH

W Netzberg wrote:
> I aggree it doesn't make much sense, but that's what I got and attached 
> a plot to prove it!
> Seems that some sort of rounding takes place, but only when I use 
> numpy.random.normal(). It is strange.

Can you post a short working and not-working (i.e. chopping off) example?

> 
> I had problems building latest version from source last night. Do you 
> know where I can find the latest rpm for fc5?
> 

No, sry. I'm still building from source myself.

-- 
cheers,
steve

Random number generation is the art of producing pure gibberish as 
quickly as possible.

W Netzberg wrote:

> I can't find a 0.87.5 rpm for fc5, might have to build it from source to 
> see if this behavior goes away... Seems to be related to numpy. If I 
> replace:
> numpy.random.normal(-0.37727, 0.1, size=10)
> with an array normal() returns, the problem goes away. Strange. Again 
> this is under 0.87.3.
> 

Hmmm I don't really get it :). You replaced 
numpy.random.normal(-0.37727, 0.1, size=10) with an array? But this 
already returns one ...

Anyway I would suggest upgrading (the latest is 0.87.7).

-- 
cheers,
steve

Random number generation is the art of producing pure gibberish as 
quickly as possible.

Apparently it was simpler than I thought:

bar (x, y, align='center', color=((0, 0, 0.5), (0, 0, 0.9), (0, 0,
0.5), (0, 0, 0.9), (0, 0, 0.5), (0, 0, 0.9), (0, 0, 0.5), (0, 0, 0.9),
(0, 0, 0.5), (0, 0, 0.9)))

does what I need.
Cheers,
Oguz


On 11/13/06, Oguz Akyuz <ogu...@gm...> wrote:
> I would like to plot a bar graph where subsequent bars have different
> colors (i.e. alternating colors). I think this will enhance the
> readability of my plot.
>
> How can I do this?
>
> Thanks,
> Oguz
>

I would like to plot a bar graph where subsequent bars have different
colors (i.e. alternating colors). I think this will enhance the
readability of my plot.

How can I do this?

Thanks,
Oguz

Ken Schutte wrote:
> Hi,
> 
> If I display a simple matrix with imshow(), e.g:
> 
> a = zeros((3,3))
> a[0,0] = 1
> imshow(a,interpolation='nearest')
> 
> the axes extend from 0.0 to 3.0 in such a way that elements are centered 
> at 0.5, 1.5,...  For example, the point at (x,y)=(.9,.9) is red, whereas 
> nearest-interp. should give a[1,1]=0.  Would it make more sense for the 
> default to be like this (as is in matlab): ?
> 
> imshow(a,interpolation='nearest',extent=(-0.5, 2.5, -0.5, 2.5))

Ken,

Actually, the matlab nearest equivalent would be
imshow(a, interpolation='nearest', extent=(-0.5, 2.5, 2.5, -0.5))
so that the y-axis increases down and both axes correspond to the array 
indices.  I agree that this makes good sense.  It seems to me that in 
the long run it would make imshow easier to explain and easier to use.

> 
> Is there a way to get behavior this automatically?

Not at present without defining your own little function to set the 
extent.  It would be easy to change imshow to work this way, so the 
question is whether enough other users would prefer it and whether it 
would cause too much disruption.  It could also be made optional via a 
new kwarg or a new interpretation of an old kwarg.  For example, extent 
could take a string to indicate this option, something like 
"extent='indices'".  An rc param could control the default.

Some discussion (and/or a ruling by John) is needed.  My preference is 
that if a change is made, it be a change in basic default behavior, not 
additional options, because any non-default behavior can be achieved 
easily using the extent kwarg in its present form, and at some point 
adding options and more complicated handling of kwargs causes more 
trouble (complex code and documentation) than it is worth.  I don't see 
any advantage of the present behavior over the matlab-equivalent 
behavior--but that may be because I am ignorant of the original rationale.

If imshow behavior is changed, a corresponding change will be needed in 
  the image-matching capability of contour.  Maybe matshow would also 
change; I haven't checked.

Eric

Hi,

If I display a simple matrix with imshow(), e.g:

a = zeros((3,3))
a[0,0] = 1
imshow(a,interpolation='nearest')

the axes extend from 0.0 to 3.0 in such a way that elements are centered 
at 0.5, 1.5,...  For example, the point at (x,y)=(.9,.9) is red, whereas 
nearest-interp. should give a[1,1]=0.  Would it make more sense for the 
default to be like this (as is in matlab): ?

imshow(a,interpolation='nearest',extent=(-0.5, 2.5, -0.5, 2.5))

Is there a way to get behavior this automatically?

Thanks,
Ken