Sorting coordinates array

[Peter Otten]

Maarten van Reeuwijk wrote:

> I'm a newbie to Python, so sorry for this maybe trivial question. I have a
> numpy array with coordinates, which I want to sort, for example first on
> z-coordinate, then x and lastly y-coordinate. So an array like:
> 
> [[0, 0, 0], [0, 2, 1], [1, 1, 0], [0, 1, 1]]
> 
> should look after sorting like
> 
> [[0, 0, 0], [1, 1, 0], [0, 1, 1], [0, 2, 1]]
> 
> I tried the sort command, but that command mangles my coordinate pairs.
> Also converting the array to a list doesn't seem to improve the results.
> How should I tackle this problem?

>>> import Numeric
>>> a = Numeric.array([[0, 0, 0], [0, 2, 1], [1, 1, 0], [0, 1, 1]])
>>> lst = a.tolist()
>>> lst.sort(lambda x, y: cmp(x[::-1], y[::-1]))
>>> lst
[[0, 0, 0], [1, 1, 0], [0, 1, 1], [0, 2, 1]]
>>>

You can pass an arbitrary comparison function to list.sort(), I just compare
reversed copies of the inner lists.
This is a highly unoptimized version, but at least seems to do the job.

Peter