[NumPy-Tickets] [NumPy] #1123: nansum for empty or all nan arrays is not zero
NumPy Trac
numpy-tickets@scipy....
Tue Jan 18 01:12:41 CST 2011
#1123: nansum for empty or all nan arrays is not zero
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Reporter: josefpktd | Owner: charris
Type: defect | Status: needs_review
Priority: normal | Milestone: 2.0.0
Component: numpy.lib | Version:
Keywords: |
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Changes (by markhmoulton@…):
* cc: markhmoulton@… (added)
Comment:
It is a mistake to define a sum of NaNs to equal zero.
Example: Ten sensors return readings on a scale of 0 to 1000, the sum of
each sensor's readings typically having a mean of 500. Half the sensors
in this case malfunction and return missing data. If a sum of NaNs is
defined to equal zero, the array of sensor sums looks something like
[500,650,350,525,725,0,0,0,0,0]. The resulting average is 275 instead of
500.
This simple error is deadly and far too frequent. We shouldn't encourage
it. By Numpy assigning the same character to all missing or invalid
values, it allows me to use only one technique (e.g., NaN masks) to catch
and remove them. If some invalid values are coded as NaN and others as
zero, I have to second-guess the programmers and do a separate check to
look for zeros and their antecedents. Ugh.
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Ticket URL: <http://projects.scipy.org/numpy/ticket/1123#comment:14>
NumPy <http://projects.scipy.org/numpy>
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