Re: [Matplotlib-users] color missing value with contourf

[Mahe <mah...@gm...>]

Benjamin Root <ben.root@...> writes:

> 
> On Tue, Feb 1, 2011 at 11:09 AM, Francesco Benincasa <francesco.benincasa-
DuY...@pu...> wrote:
> 
> Hi all,
> I'm using pygrads for plotting maps from netcdf files.
> I use the contourf method, but I'm not able to fill the region where there are
> no value (there is the missing value -999) with a color. It seems to ignore
> the set_bad method that I used to make the colormap.
> Any suggestions?
> Thank you very much in advance.
> --
> | Francesco Benincasa
> 
> 
> Most likely, the issue is that set_bad is more for setting the color when 
encountering masked values (through masked arrays).  As a quick and dirty way to 
deal with it, try setting that color through the set_under() method.The correct 
way to do this is to use set_bad, but convert  your numpy array that you are 
displaying into a masked array like so:z_ma = np.ma.masked_array(z, mask=(z == 
-999))and use contourf on z_ma.Let us know how that works for you.Ben Root
> 
> 
> 
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Hi !
I have had the same issue (set_bad not taking effect with nans), and transformed 
the data into a masked array. But it does not seem to work...
Here a minimal example:

import matplotlib.pyplot as plt
import numpy as np

plt.clf()
x = np.linspace(-180,180,100)
y = np.linspace(-90,90,100)
x, y = np.meshgrid(x,y)
data = np.cos(x/180*np.pi) + np.sin(y/180*np.pi)
data[(y<50)&(y>30)&(x<50)&(x>30)] = np.nan
data = np.ma.masked_array(data, mask = np.isnan(data)) # has no effect
ncol = 20
cbar = [-1,1]
palette = plt.cm.Blues
palette.set_bad('green')
palette.set_over('red')
palette.set_under('black')
cs = plt.contourf(x,y,data,np.linspace(cbar[0],cbar[1],ncol), cmap=palette, 
extend='both')
plt.colorbar()
cs.set_clim(cbar) # need that for set_upper and set_lower to take effect
plt.show()

There is already that small bug where one needs to call set_clim for set_upper 
and set_lower, maybe something similar is needed for set_bad?
Any idea?

Many thanks,
Mahe