[Matplotlib-users] Significance of this error message in matplotlib context?

[Kevin M. <kjm...@at...>]

If anyone could assist me in understanding what issues result in the error 
message below , I would be very grateful.

"Cannot automatically convert masked array to Numeric because data
                   is masked in one or more locations"
(error raised by Numeric, but within matplotlib core)

I frequently run into this error message when I try to use matplotlib to 
produce contour graphs.  Does anyone have a more detailed explanation of what 
issues prompt this error?  What confuses me is that the same script (posted 
below, FWIW) may or may not produce this error depending on which datafile I 
try to graph?  I also get this message if I use the Numeric function where() 
to generate any array used by the contour() function.

Thanks,
    Kevin Mueller
    Univ. Illinois, Dept. Atmospheric Sciences, Urbana/Champaign

#######################

traceback:
(python 2.4.1, Numeric 24b, matplotlib 0.80, linux)

#######################

Traceback (most recent call last):
  File "/home/manabe/a/kjmuelle/scripts/latlonslice.py", line 39, in ?
    badmask=outmask,cmap=cm.jet,colors=None)
  File 
"/home/manabe/a/kjmuelle/lib/python2.4/site-packages/matplotlib/toolkits/basemap/basemap.py", 
line 1030, in contourf
    levels, colls = pylab.contourf(*args, **kwargs)
  File 
"/home/manabe/a/kjmuelle/lib/python2.4/site-packages/matplotlib/pylab.py", 
line 1679, in contourf
    ret =  gca().contourf(*args, **kwargs)
  File 
"/home/manabe/a/kjmuelle/lib/python2.4/site-packages/matplotlib/axes.py", 
line 1248, in contourf
    return self._contourHelper.contourf(*args, **kwargs)
  File 
"/home/manabe/a/kjmuelle/lib/python2.4/site-packages/matplotlib/contour.py", 
line 879, in contourf
    lev, cmap)
  File 
"/home/manabe/a/kjmuelle/lib/python2.4/site-packages/matplotlib/contour.py", 
line 629, in _process_colors
    mappable.autoscale()
  File "/home/manabe/a/kjmuelle/lib/python2.4/site-packages/matplotlib/cm.py", 
line 456, in autoscale
    self.norm.autoscale(self._A)
  File 
"/home/manabe/a/kjmuelle/lib/python2.4/site-packages/matplotlib/colors.py", 
line 580, in autoscale
    rval = ravel(A)
  File 
"/home/manabe/a/kjmuelle/lib/python2.4/site-packages/Numeric/Numeric.py", 
line 543, in ravel
    return reshape(m, (-1,))
  File "/home/manabe/a/kjmuelle/lib/python2.4/site-packages/Numeric/MA/MA.py", 
line 632, in __array__
    raise MAError, \
MA.MA.MAError: Cannot automatically convert masked array to Numeric because 
data
                   is masked in one or more locations.

############################

WHEN RUNNING THIS SCRIPT:

############################

from Scientific.IO import NetCDF as nc
import Numeric as nm
from pylab import *
import sys,os.path


it=0 # time index
ik=0 # depth index
tracer="DIC" # tracer name

if not len(sys.argv)>1:
    print "Error: no datafile arguments given"
else:
    datapaths = sys.argv[1:]

for datapath in datapaths:
    f = nc.NetCDFFile(datapath)
    outdata = f.variables[tracer].getValue()[it,ik,:,:]
    outmask = f.variables["TMASK"].getValue()[ik,:,:]
    gdepth = f.variables["z_t"].getValue()
    f.close()

    X,Y,Z = nm.arange(-180,181,4),nm.arange(-90,91,2),gdepth*.01

    clf()

    levels,colors = contourf(X,Y,outdata,
                               badmask=outmask,cmap=cm.jet,colors=None)
    levels,colors = contour(X,Y,outdata,
                              badmask=outmask,colors='k')
    colorbar(tickfmt="%.1e")

    gtitle = "%s: at depth %i, %s" % (os.path.split(datapath[1],-Z[ik],tracer)
    title(gtitle)
    show()