On Mar 13, 2014, at 9:39 AM, Nicolas Rougier <[email protected]> wrote:
> > Seems to be related to the masked values: Good hint -- a masked array keeps the "junk" values in the main array. What "abs" are you using -- it may not be mask-aware. ( you want a numpy abs anyway) Also -- I'm not sure I know what happens with Boolean operators on masked arrays when you use them to index. I'd investigate that. (sorry, not at a machine I can play with now) Chris > print r2010[:3,:3] > [[-- -- --] > [-- -- --] > [-- -- --]] > > print abs(r2010)[:3,:3] > [[-- -- --] > [-- -- --] > [-- -- --]] > > > print r2010[ r2010[:3,:3] <0 ] > [-- -- -- -- -- -- -- -- --] > > print r2010[ abs(r2010)[:3,:3] < 0] > [] > > Nicolas > > > > On 13 Mar 2014, at 16:52, Sudheer Joseph <[email protected]> wrote: > >> Dear experts, >> I am encountering a strange behaviour of python data >> array as below. I have been trying to use the data from a netcdf >> file(attached herewith) to do certain calculation using below code. If I >> take absolute value of the same array and look for values <.5 I get a >> different value than the original array. But the fact is that this >> particular case do not have any negative values in the array( but there are >> other files where it can have negative values so the condition is put). I do >> not see any reason for getting different numbers for values <.5 in case of >> bt and expected it to be same as that of r2010. If any one has a guess on >> what is behind this behaviour please help. >> >> >> In [14]: from netCDF4 import Dataset as nc >> >> In [15]: nf=nc('r2010.nc') >> In [16]: r2010=nf.variables['R2010'][:] >> In [17]: bt=abs(r2010) >> In [18]: bt[bt<=.5].shape >> Out[18]: (2872,) >> In [19]: r2010[r2010<.5].shape >> Out[19]: (36738,) >> >> >> bt.min() >> Out[20]: 0.0027588337040836768 >> >> In [21]: bt.max() >> Out[21]: 3.5078965479057089 >> In [22]: r2010.max() >> Out[22]: 3.5078965479057089 >> In [23]: r2010.min() >> Out[23]: 0.0027588337040836768 >> >> >> >> *************************************************************** >> Sudheer Joseph >> Indian National Centre for Ocean Information Services >> Ministry of Earth Sciences, Govt. of India >> POST BOX NO: 21, IDA Jeedeemetla P.O. >> Via Pragathi Nagar,Kukatpally, Hyderabad; Pin:5000 55 >> Tel:+91-40-23886047(O),Fax:+91-40-23895011(O), >> Tel:+91-40-23044600(R),Tel:+91-40-9440832534(Mobile) >> E-mail:[email protected];[email protected] >> Web- http://oppamthadathil.tripod.com >> ***************************************************************<r2010.nc>_______________________________________________ >> NumPy-Discussion mailing list >> [email protected] >> http://mail.scipy.org/mailman/listinfo/numpy-discussion > > _______________________________________________ > NumPy-Discussion mailing list > [email protected] > http://mail.scipy.org/mailman/listinfo/numpy-discussion _______________________________________________ NumPy-Discussion mailing list [email protected] http://mail.scipy.org/mailman/listinfo/numpy-discussion
