[Numpy-discussion] problem with assigning to recarrays

Brian Gerke bgerke@slac.stanford....
Fri Feb 27 19:06:33 CST 2009


On Feb 27, 2009, at 4:30 PM, Robert Kern wrote:
>>
> r[where(r.field1 == 1.)] make a copy. There is no way for us to
> construct a view onto the original memory for this circumstance given
> numpy's memory model.

Many thanks for the quick reply.  I assume that this is true only for  
record arrays, not for ordinary arrays?  Certainly I can make an  
assignment in this way with a normal array.

Also, if it is truly impossible to change this behavior, or to have it  
raise an error--then are there any best-practice suggestions for how  
to remember and avoid running into this non-obvious behavior?  If one  
thinks of record arrays as inheriting  from numpy arrays, then this  
problem is certainly unexpected.


Also, I've just found that the following syntax does do what is  
expected:

(r.field2)[where(field1 == 1.)] = 1.

It is at least a little aesthetically displeasing that the syntax  
works one way but not the other.  Perhaps my best bet is to stick with  
this syntax and forget that the other exists?  A less-than-satisfying  
solution, but workable.

Brian

>
>
> r[where(r.field1 == 1.)].field2 = 0.0 assigns to the copy.
>
> -- 
> Robert Kern
>
> "I have come to believe that the whole world is an enigma, a harmless
> enigma that is made terrible by our own mad attempt to interpret it as
> though it had an underlying truth."
>  -- Umberto Eco
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