[Numpy-discussion] finding close together points.

Christopher Barker Chris.Barker at noaa.gov
Thu Nov 12 14:52:39 EST 2009

Robert Kern wrote:

> Didn't we already do this?
> http://www.mail-archive.com/numpy-discussion@scipy.org/msg21010.html

Indeed we did. What I posted then ( and have improved a bit now). Is a 
Python version. Written in Python, it has an advantage of using less 
memory for a big array, but is slower in other respects than a Python 
list. This is probably why we all use lists for this when we need it!

What I'd like (and I have seen interest from others) is a C version, one 
that could be used from C code directly as well. I can't benchmark that, 
as it hasn't been written!

I'm afraid I'm out of my depth as to how to write such a thing in C (at 
least so that it is well integrated into numpy). I suppose I could write 
a simple C accumulating array, and only convert it into a numpy array at 
the end (indeed, I have done that in the past), and benchmark that.

Charles R Harris wrote:

> I'm rapidly losing interest here.

Maybe that's why it hasn't been done yet -- it's not an interesting 
enough problem!

>  Why not just a class using an array that 
> doubles the array size when an index is out of bounds and copies over 
> the old data.

Yes, it pretty much is that simple -- that's my point. Simple and 
useful, and why should we all re-invent this wheel each time (even it if 
is a simple wheel)? At the C(ython) level, it's not that hard to simply 
do your accumulating in regular old C, and then convert to a numpy 
array, but it would be nice for it to be easier, particularly for 
various data-neutral code, particularly numpy custom-defined ones.


Christopher Barker, Ph.D.

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