On Mar 13, 2014, at 9:39 AM, Nicolas Rougier <Nicolas.Rougier@inria.fr> 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 <sudheer.joseph@yahoo.com> 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:sjo.India@gmail.com;sudheer.joseph@yahoo.com Web- http://oppamthadathil.tripod.com ***************************************************************<r2010.nc>_______________________________________________ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
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