matplotlib-users

[Matplotlib-users] How to use logarithmic scale with histogram?

[<mik...@gm...>]

Hi!
I'm trying to generate some kind of "distribution" view / histogram
of decimal numbers, i.e. i want the graph to indicate exactly how many times
any given decimal number occurs in "x". As an example, i've set the values
to tuple "x" as seen in the code snipplet below. In reality there will be at
least couple of thousand decimal values or more in the tuple (x in this
example) and values will be retrieved from file etc. This code does seem to
draw some kind of histogram but it would be much more usefull to have at
least the y-scale as logarithmic. But I haven't found a way to make the
scale logarithmic. I've tried to use semilogy/semilogx/loglog but with no
success.

---------------
x=0.000925,0.000879,0.000926,0.00088,0.001016,0.000931,0.000927,0.00088,
0.000926,0.000926,0.000879,0.0009
n, bins, patches = hist(x, 1000)
l = plot(bins, n, 'r--')
grid(True)
show()
----------------

regards, Mika

Re: [Matplotlib-users] How to use logarithmic scale with histogram?

[Matthias M. <Mat...@gm...>]

Hi Mika,=20
Hi everybody,

I'm not sure I really understand your problem, but I attached my proposal /=
=20
solution, so you can think about it or maybe describe your problem once mor=
e.

Much success,

Matthias Michler

>--------------------------------------------------------------------------=
=2D-----------------------
from pylab import figure, subplot, grid, close, show,\
                  hist, plot, semilogy, nonzero

x =3D 0.000925, 0.000879, 0.000926, 0.00088, 0.001016, 0.000931, 0.000927, \
    0.00088, 0.000926, 0.000926, 0.000879, 0.0009
figure(0)                                 # make histogram in figure 0
n, bins, patches =3D hist(x, 1000, align=3D'center')
close(0)                                 # close figure to delete plot
                                              #  instance of hist
index =3D nonzero(n)                # to solve problems mit zero
                                              # values in log scale
figure(1)
ax =3D subplot(111)
ax.set_yscale('log')
l1 =3D plot(bins[index], n[index], ls=3D'',marker =3D'x', ms=3D15, mew=3D3,=
 c=3D'r')
grid(True)
figure(2)
l2 =3D semilogy(bins[index], n[index], ls=3D'',marker =3D'x', ms=3D15, mew=
=3D3, c=3D'r')
grid(True)
show()
>--------------------------------------------------------------------------=
=2D------------------------

On Tuesday 06 February 2007 15:33, Mika Oraj=E4rvi wrote:
> Hi!
> I'm trying to generate some kind of "distribution" view / histogram
> of decimal numbers, i.e. i want the graph to indicate exactly how many
> times any given decimal number occurs in "x". As an example, i've set the
> values to tuple "x" as seen in the code snipplet below. In reality there
> will be at least couple of thousand decimal values or more in the tuple (x
> in this example) and values will be retrieved from file etc. This code do=
es
> seem to draw some kind of histogram but it would be much more usefull to
> have at least the y-scale as logarithmic. But I haven't found a way to ma=
ke
> the scale logarithmic. I've tried to use semilogy/semilogx/loglog but with
> no success.
>
> ---------------
> x=3D0.000925,0.000879,0.000926,0.00088,0.001016,0.000931,0.000927,0.00088,
> 0.000926,0.000926,0.000879,0.0009
> n, bins, patches =3D hist(x, 1000)
> l =3D plot(bins, n, 'r--')
> grid(True)
> show()
> ----------------
>
> regards, Mika

Re: [Matplotlib-users] How to use logarithmic scale with histogram?

[<jk...@ik...>]

"Mika Orajärvi" <mik...@gm...> writes:

> This code does seem to draw some kind of histogram but it would be
> much more usefull to have at least the y-scale as logarithmic. But I
> haven't found a way to make the scale logarithmic.

According to the docstring of hist you can give it a keyword argument
of log=True to make the y axis logarithmic. However there is a slight
bug in that zero-height histogram bars like you have in your example
cause log(0) to be computed. Here's a quick fix:

------------------------------------------------------------------------
from pylab import *
x=0.000925,0.000879,0.000926,0.00088,0.001016,0.000931,0.000927,0.00088,\
  0.000926,0.000926,0.000879,0.0009
n, bins = mlab.hist(x, 1000)
width = 0.9 * (bins[1]-bins[0])
nz = nonzero(n)
bar(bins[nz], n[nz], width=width, log=True)
grid(True)
show()
------------------------------------------------------------------------

If the devs agree that this is a bug in hist, I can fix it in svn.

-- 
Jouni K. Seppänen
http://www.iki.fi/jks

Re: [Matplotlib-users] How to use logarithmic scale with histogram?

[Eric F. <ef...@ha...>]

Jouni K. Seppänen wrote:
> "Mika Orajärvi" <mik...@gm...> writes:
> 
>> This code does seem to draw some kind of histogram but it would be
>> much more usefull to have at least the y-scale as logarithmic. But I
>> haven't found a way to make the scale logarithmic.
> 
> According to the docstring of hist you can give it a keyword argument
> of log=True to make the y axis logarithmic. However there is a slight
> bug in that zero-height histogram bars like you have in your example
> cause log(0) to be computed. Here's a quick fix:
> 
> ------------------------------------------------------------------------
> from pylab import *
> x=0.000925,0.000879,0.000926,0.00088,0.001016,0.000931,0.000927,0.00088,\
>   0.000926,0.000926,0.000879,0.0009
> n, bins = mlab.hist(x, 1000)
> width = 0.9 * (bins[1]-bins[0])
> nz = nonzero(n)
> bar(bins[nz], n[nz], width=width, log=True)
> grid(True)
> show()
> ------------------------------------------------------------------------
> 
> If the devs agree that this is a bug in hist, I can fix it in svn.
> 

I think it is already fixed.  This works (drawing a sensible bar plot 
with a log scale despite bins with zero):

In [3]:hist(rand(10), log=True)
Out[3]:
(array([1, 0, 3, 1, 0, 1, 2, 1, 0, 1]),
  array([ 0.00863515,  0.10200932,  0.19538349,  0.28875767,  0.38213184,
         0.47550601,  0.56888018,  0.66225435,  0.75562852,  0.84900269]),
  <a list of 10 Patch objects>)

Eric