[Numpy-discussion] Resizing without allocating additional memory
Travis Oliphant
oliphant at ee.byu.edu
Wed Dec 6 12:45:03 CST 2006
David Huard wrote:
> Hi,
>
> I have fortran subroutines wrapped with f2py that take arrays as
> arguments, and I often need to use resize(a, N) to pass an array of
> copies of an element. The resize call , however, is becoming the speed
> bottleneck, so my question is:
> Is it possible to create an (1xN) array from a scalar without
> allocating additional memory for the array, ie just return a new
> "view" of the array where all elements point to the same scalar.
>
I don't think this would be possible in Fortran because Fortran does not
provide a facility for using arbitrary striding (maybe later versions of
Fortran using pointers does, though).
If you can use arbitrary striding in your code, then you can construct
such a view using appropriate strides (i.e. a stride of 0). You can do
this with the ndarray constructor:
a = array(5)
g = ndarray(shape=(1,10), dtype=int, buffer=a, strides=(0,0))
But, notice you will get interesting results using
g += 1
Explain why the result of this is an array of 15 (Hint: look at the
value of a).
-Travis
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