Arthur,
I wrote the date2index function and I think what you are seeing is a bug
that I fixed a couple of months ago. By using the latest version of
netcdf4-python, not only should this bug disappear, but you'll also find
that date2index now supports different selection methods: 'exact', 'before',
'after', 'nearest', that should help with your use case.
If this does not fix the problem you are seeing, I'd appreciate having a
copy of the file and code to reproduce the problem and find a solution.
HTH,
David Huard
On Mon, Sep 7, 2009 at 9:27 AM, Arthur M. Greene <a...@iri.columbia.edu>wrote:
> Hi All,
>
> The problem is not with fetching the data slice itself, but finding the
> correct indices to specify, particularly with the time dimension. The
> below examples refer to a remote dataset that I can open and slice using
> indices, as in
>
> slice = remoteobj.variables['tas'][:120,20:40,30:50].
>
> However, I have problems when trying to use the syntax in plotsst.py or
> pnganim.py (from the examples) to find time indices:
>
> In [107]: from datetime import datetime as dt
> In [108]: date0 = dt(1951,1,1,0)
> In [110]: print date0
> 1951-01-01 00:00:00
>
> In [125]: timedata = remoteobj.variables['time']
> In [126]: nt0 = date2index(date0,timedata)
> ---------------------------------------------------------------------------
> AssertionError Traceback (most recent call last)
>
> /home/amg/work/nhmm/<ipython console> in <module>()
>
>
> /usr/local/cdat/trunk/lib/python2.5/site-packages/mpl_toolkits/basemap/__init__.pyc
>
> in date2index(dates, nctime, calendar)
> 3924 Returns an index or a sequence of indices.
> 3925 """
> -> 3926 return netcdftime.date2index(dates, nctime, calendar=None)
> 3927
> 3928 def maskoceans(lonsin,latsin,datain,inlands=False):
>
>
> /usr/local/cdat/trunk/lib/python2.5/site-packages/mpl_toolkits/basemap/netcdftime.pyc
>
> in date2index(dates, nctime, calendar)
> 986
> 987 # Perform check again.
> --> 988 _check_index(index, dates, nctime, calendar)
> 989
> 990 # convert numpy scalars or single element arrays to python
> ints.
>
>
> /usr/local/cdat/trunk/lib/python2.5/site-packages/mpl_toolkits/basemap/netcdftime.pyc
>
> in _check_index(indices, dates, nctime, calendar)
> 941 for n,i in enumerate(indices):
> 942 t[n] = nctime[i]
> --> 943 assert numpy.all( num2date(t, nctime.units, calendar) == dates)
> 944
> 945
>
> AssertionError:
>
> ---------------------------------------------------------
>
> It turns out that date0 corresponds best to index 1080:
>
> In [139]: remoteobj.variables['time'][1080]
> Out[139]: 32865.5
>
> In [141]: num2date(32865.5,timedata.units,timedata.calendar)
> Out[141]: 1951-01-16 12:00:00
>
> This isn't the _exact_ date and time I had specified, but
>
> In [142]: date0 = dt(1951,01,16,12,00,00)
> In [143]: print date0
> 1951-01-16 12:00:00
>
> In [144]: date2index(date0,timedata,timedata.calendar)
>
> produces the same AssertionError. Where is the problem?
>
> What I would _like_ to do is to issue a simple call using coordinates
> rather than the indices, of the form:
>
> slice = variable[date0:date1,[plev],lat0:lat1,lon0:lon1],
>
> or similar, preferably without writing a whole module just to find the
> correct indices. I need to fetch similar slices from a group of models,
> having time axes that may each be defined slightly differently --
> different calendars, time point set at a different day of the month,
> etc. (It's monthly data and I'm specifying only monthly bounds, even
> though the calendar may be defined as "days since 1860...") I need to
> automate the process so I get back the correct slab regardless.
>
> Suggestions appreciated!
>
> Thx,
>
> Arthur
>
>
> *^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*
> Arthur M. Greene, Ph.D.
> The International Research Institute for Climate and Society (IRI)
> The Earth Institute, Columbia University, Lamont Campus
>
> amg at iri dot columbia dot edu | http://iri.columbia.edu
> *^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*^*~*
>
>
>
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