matplotlib-users Mailing List for matplotlib

Am 19.10.2012 23:26, schrieb Damon McDougall:
> Correct me if I'm wrong, but I don't even think you need them. I think
> the default cmap behaviour is to normalise to the min and max of the
> data.

yes, default cmap behaviour will normalise to the min and max of the
data.

On Fri, Oct 19, 2012 at 10:23 PM, Daπid <dav...@gm...> wrote:
> On Fri, Oct 19, 2012 at 11:08 PM, elmar werling <el...@ne...> wrote:
>> vmin=min(z), vmax=max(z)
>
> A suggestion, when dealing with arrays, it is generally faster to use
> the numpy function to compute the max and min, either np.max(z) or
> z.max(), than the standard Python one.

Correct me if I'm wrong, but I don't even think you need them. I think
the default cmap behaviour is to normalise to the min and max of the
data.

-- 
Damon McDougall
http://www.damon-is-a-geek.com
B2.39
Mathematics Institute
University of Warwick
Coventry
West Midlands
CV4 7AL
United Kingdom

On Fri, Oct 19, 2012 at 11:08 PM, elmar werling <el...@ne...> wrote:
> vmin=min(z), vmax=max(z)

A suggestion, when dealing with arrays, it is generally faster to use
the numpy function to compute the max and min, either np.max(z) or
z.max(), than the standard Python one.

thanks for help,

finally I found the following solution

elmar


import numpy as np
import matplotlib as mpl
import matplotlib.pyplot as plt

N = 200
x = np.linspace(0,1,N)
y = np.random.randn(N)
z = np.random.randn(N)*2+5

cm = mpl.cm.get_cmap('RdYlBu')
sc = plt.scatter(x, y, c=z, vmin=min(z), vmax=max(z), s=35, cmap=cm)
plt.colorbar(sc)

plt.show()



Am 19.10.2012 21:59, schrieb Joe Kington:
>      plt.scatter(x, y, c=z, marker='s')
>      plt.colorbar()

That's what ``scatter`` is intended for.

Basically, you want something like:

    plt.scatter(x, y, c=z, marker='s')
    plt.colorbar()

Note that you can also vary the markers by size based on an additional
parameter, as well.

Have a look at this example:
http://matplotlib.org/examples/pylab_examples/scatter_demo.html

Hope that helps,
-Joe


On Fri, Oct 19, 2012 at 2:19 PM, elmar werling <el...@ne...> wrote:

> Hi,
>
> is there a way to adjust the marker color in a xy-plot in relation to
> the value of a third parameter. Something as the following - not working
> - example 1.
>
> Example 2 is working but rather slow for large arrays.
>
> cheers
> Elmar
>
>
>
>
> # example 1
>
> import matplotlib.pyplot as plt
>
> x = [1,2,3,4]
> y = x
> c = ((1.0, 0.0, 0.0), (0.8, 0.1, 0.1), (0.6, 0.2, 0.6), (0.4, 0.3, 0.3))
>
> plt.plot(x,y, color=c, marker='s')
> plt.show()
>
>
> example 2:
>
> import matplotlib.pyplot as plt
>
> x = [1,2,3,4]
> y = x
> c = ((1.0, 0.0, 0.0), (0.8, 0.1, 0.1), (0.6, 0.2, 0.6), (0.4, 0.3, 0.3))
>
> for i in range(len(x)):
>      plt.plot(x[i], y[i], color=c[i], marker='s')
>
> plt.show()
>
>
>
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Hi,

is there a way to adjust the marker color in a xy-plot in relation to 
the value of a third parameter. Something as the following - not working 
- example 1.

Example 2 is working but rather slow for large arrays.

cheers
Elmar




# example 1

import matplotlib.pyplot as plt

x = [1,2,3,4]
y = x
c = ((1.0, 0.0, 0.0), (0.8, 0.1, 0.1), (0.6, 0.2, 0.6), (0.4, 0.3, 0.3))

plt.plot(x,y, color=c, marker='s')
plt.show()


example 2:

import matplotlib.pyplot as plt

x = [1,2,3,4]
y = x
c = ((1.0, 0.0, 0.0), (0.8, 0.1, 0.1), (0.6, 0.2, 0.6), (0.4, 0.3, 0.3))

for i in range(len(x)):
     plt.plot(x[i], y[i], color=c[i], marker='s')

plt.show()

Good idea. If the png version works then the jpg version should also be
made to work,

Would you be willing to open up an issue for the feature request? :
https://github.com/matplotlib/matplotlib/issues/new

If your ready and willing to implement such a thing, that would be even
better (just open a pull request and we can start reviewing)!

All the best,

Phil



On 19 October 2012 15:59, Rich Signell <rsi...@us...> wrote:

> MPL folks,
>
> Would it be possible to enhance Matplotlib to allow "im=imread(url)"
> to work if url returns a JPG?
>
> Currently (it seems):
>
> 1. If the URL returns a PNG this works:
>
> im = imread(urllib2.urlopen(url))
>
> 2. If the URL returns a JPG, this DOESN'T work:
>
> im = imread(urllib2.urlopen(url))
>
> .. and neither does this:
> im = imread(urllib2.urlopen(url),format='jpg')
>
> ... but this DOES work:
>
> im = Image.open(cStringIO.StringIO(urllib.urlopen(url).read()))
>
> See an example in Ipython Notebook here:
> http://nbviewer.ipython.org/3918576/
>
> So could just be hidden from the user so that "im = imread(url)" would
> just work for JPG (assuming PIL was installed)?
>
> Thanks,
> Rich
> --
> Dr. Richard P. Signell
> USGS, 384 Woods Hole Rd.
> Woods Hole, MA 02543-1598
>
>
> ------------------------------------------------------------------------------
> Everyone hates slow websites. So do we.
> Make your web apps faster with AppDynamics
> Download AppDynamics Lite for free today:
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> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
>

Hi,

Le 19/10/2012 06:48, Jae-Joon Lee a écrit :
> Figuring out the dpi of the screen, I have no clue at this moment.
> Maybe this is something a gui expert can answer.
I'm certainly not a gui expert, but as a PyQt user, I know screen
resolution is indeed Python-accessible with PyQt. (I guess other
toolkits provide their own methods)

I've made a quick script that prints the screen X and Y resolution
(requires PyQt). Reference links to PyQt API docs are included.


In my case, it's 96 dpi, and that what I use in my matplotlibrc file for
the "figure.dpi" property. But I use a higher value (say 150) for
"savefig.dpi" so that I get better resolution when saving PNG images.

I agree with Nikolaus that the dpi value for displaying figures would be
better get by the software, if possible. Maybe a property like
figure.dpi='auto' should activate such a behavior. But this would
require many code duplicates, one for each gui toolkit.


Best,
Pierre

MPL folks,

Would it be possible to enhance Matplotlib to allow "im=imread(url)"
to work if url returns a JPG?

Currently (it seems):

1. If the URL returns a PNG this works:

im = imread(urllib2.urlopen(url))

2. If the URL returns a JPG, this DOESN'T work:

im = imread(urllib2.urlopen(url))

.. and neither does this:
im = imread(urllib2.urlopen(url),format='jpg')

... but this DOES work:

im = Image.open(cStringIO.StringIO(urllib.urlopen(url).read()))

See an example in Ipython Notebook here:
http://nbviewer.ipython.org/3918576/

So could just be hidden from the user so that "im = imread(url)" would
just work for JPG (assuming PIL was installed)?

Thanks,
Rich
-- 
Dr. Richard P. Signell
USGS, 384 Woods Hole Rd.
Woods Hole, MA 02543-1598

> Yeah, that's what I feared. But in the mean time, are there any best
> practices to minimize undesired effects like the one above? For example,
> are there any other functions that need special parameters to not raster
> their output when writing to a vector format? And is there a way to get
> a figure on the screen with the right size when I don't know what dpi
> the monitor is running with?

As I said, if you use interpolation="none" with your inshow, the
original image will be sent to the backends.

Figuring out the dpi of the screen, I have no clue at this moment.
Maybe this is something a gui expert can answer.

Regards,

-JJ

On Tue, Oct 16, 2012 at 4:04 PM, T J <tj...@gm...> wrote:
> I'm interested in clipping the result of plt.contour (and
> plt.contourf) to a patch.  However, QuadContourSet does not have a
> set_clip_path() method.  Is there a way to do this?

QuadContourSet does not (I think it should), but LineCollection
instances in QuadContourSet.collections does. Below is a quick
example.

import matplotlib.pyplot as plt
import numpy as np

x = np.arange(100)-50
arr = (x**2 + x[:,np.newaxis]**2)**.5
cont = plt.contour(arr)
col1 = cont.collections[3] # contour line to clip with.
clip_path = col1.get_paths()[0] # Note that col1 may have multiple paths.
for col in cont.collections:
    col.set_clip_path(clip_path, col1.get_transform()) # set clip_path
for individual LineCollection instances.

plt.show()