On 05/09/2010 09:01 AM, Gökhan Sever wrote:
>
>
> On Fri, May 7, 2010 at 3:28 PM, Pierre GM <[email protected]
> <mailto:[email protected]>> wrote:
>
> On May 4, 2010, at 8:38 PM, Gökhan Sever wrote:
> > Hello,
> >
> > I have the following arrays read as masked array.
> >
> > I[10]: basic.data['Air_Temp'].mask
> > O[10]: array([ True, False, False, ..., False, False, False],
> dtype=bool)
> >
> > [12]: basic.data['Press_Alt'].mask
> > O[12]: False
> >
> > I[13]: len basic.data['Air_Temp']
> > -----> len(basic.data['Air_Temp'])
> > O[13]: 1758
> >
> >
> > The first item data['Air_Temp'] has only the first element masked
> and this result with mask attribute being created an equal data
> length bool array. On the other hand data['Press_Alt'] has no
> elements to mask yielding a 'False' scalar. Is this a documented
> behavior or intentionally designed this way? This is the only case
> out of 20 that breaks my code as following: :)
> >
> > IndexError Traceback (most recent
> call last)
> >
> > 130 for k in range(len(shorter)):
> > 131 if (serialh.data['dccnTempSF'][k] != 0) \
> > --> 132 and (basic.data['Air_Temp'].mask[k+diff] == False):
> > 133 dccnConAmb[k] = serialc.data['dccnConc'][k] * \
> > 134
> physical.data['STATIC_PR'][k+diff] * \
> >
> > IndexError: invalid index to scalar variable.
> >
> > since mask is a scalar in this case, nothing to loop terminating
> with an IndexError.
>
>
> Gokhan,
> Sorry for not getting back sooner, web connectivity was limited on
> my side.
> I must admit I can't really see what you're tring to do here, but
> I'll throw some random comments:
> * If you're using structured MaskedArrays, it's a really bad idea to
> call one of the fields "data", as it may interact in a non-obvious
> way with the actual "data" property (the one that outputs a view of
> the array as a pure ndarray).
>
>
> Hello Pierre,
>
> basic.data is a dictionary containing all masked array items. When I
> read the original data into scripts, my main constructor-reader class
> automatically converts data to masked arrays. basic.data['Air_Temp'] is
> a masked array itself, little confusing for sure it also has 'data'
> attribute.
>
> In the above example I check one condition looping in mask value. When
> mask attribute isn't an bool-array (when there is no missing value in
> data) the condition fails asserting an IndexError. I was wondering why
> it doesn't yield a bool-array instead of giving me a scalar False.
The mask attribute can be a full array, or it can be a scalar to
indicate that nothing is masked. This is an optimization in masked
arrays; it adds complexity, but it can save space and/or processing
time. You can always access a full mask array by using
np.ma.getmaskarray(). Or you can ensure the internal mask is an array,
not a scalar, by using the shrink=False kwarg when making the masked
array with np.ma.array().
Offhand, I suspect your loop can be eliminated by vectorization.
Something like this:
ns = len(shorter)
slice0 = slice(ns)
slice1 = slice(diff, diff+ns)
cond1 = serialh.data['dccnTempSF'][slice0] != 0
cond2 = np.ma.getmaskarray(basic.data['Air_Temp'][slice1]) == False
cond = cond1 & cond2
dccnConAmb[slice0][cond] = (serialc.data['dccnConc'][slice0][cond] *
physical.data['STATIC_PR'][slice1][cond])
Eric
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