Re: [Matplotlib-users] Data plotting in a wrong place

[Jason S. <jas...@gm...>]

On Thu, 2014-06-26 at 23:14 -0700, billyi wrote:
> Oh my, it WAS the meshgrid! Thank you so much! 
> When reading the coordinates like:
> lat = FB.variables['lat'][:,:]
> lon = FB.variables['lon'][:,:]
> 
> And plotting (without meshgrid!):
> m.pcolormesh(lon, lat, masked_fb, latlon=True)
> 
> it works! Now I feel stupid.
> And I think the longitudes and latitudes are not monotonic, but I don't know
> the way to check this, other than checking the array like lon[:] in
> terminal. Is there a better way?

Yes.  Consider:

py> all(lon[:-1] <= lon[1:])

If True, then lon is monotonically increasing.  Otherwise it's not.

Description:

lon[:-1] is a slice that takes every element of lon except the last one.
lon[1:] is a slice that takes every element of lon except the first one.
The comparison operator will create a bool numpy array whose elements
will be True for each element "i" if the i'th element is less than or
equal to the i+1'th element.  Applying the "all" (or numpy.all)
functions to this bool array will return True if every element is true
and False otherwise.

Faster, easier, and less error-prone than printing out the array and
checking it yourself.  Of course you could do something more explicit:

py> monotonic = True
py> for i in range(len(lon)-1):
py>     if lon[i] > lon[i+1]:
py>         monotonic = False
py>         break

HTH,
Jason