[Numpy-discussion] Need help for implementing a fast clip in numpy (was slow clip)
David Cournapeau
david at ar.media.kyoto-u.ac.jp
Fri Jan 12 00:52:41 CST 2007
Travis Oliphant wrote:
>
> This is one thing I've exposed (and made use of in more than one place)
> with NumPy. In Numeric, the magic was in a few lines of the ufuncobject
> file). Now, it is exposed in the concept of an array iterator. Anybody
> can take advantage of it as it there is a C-API call to get an array
> iterator from the array (it's actually the object returned by the .flat
> method). You can even get an iterator that iterates over one-less
> dimension than the array has (with the dimension using the smallest
> strides left "un-iterated" so that you can call an inner loop with it).
The thing which confuses me is whether this is useful when you only one
item of one array at a time. When I was implementing some functions for
LPC, I took a look at your examples for array iterators and explanations
in the numpy ebook, and it looked really helpful, indeed. For this kind
of code, I needed to operate on several contiguous elements at a time.
But here, for cliping with scalar min and max, I only need to access to
one item at a time from the input array, and that's it; in particular, I
don't care about the order of iteration. So the question really boils
down to:
"for a numpy array a of eg float32, am I guaranteed that
a->data[sizeof(float32) * i] for 0 <= i < a.size gives me all the items
of a, even for non contiguous arrays ?"
cheers,
David
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