Sorting coordinates array

[Maarten van Reeuwijk]

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?

TIA, Maarten

--
================================================== =================
Maarten van Reeuwijk Heat and Fluid Sciences
Phd student dept. of Multiscale Physics
www.ws.tn.tudelft.nl Delft University of Technology

[Ville Vainio]

Maarten van Reeuwijk <maarten@remove_this_ws.tn.tudelft.nl> writes:

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:

Implement a comparison function:

help([].sort)

Help on built-in function sort:

sort(...)
L.sort(cmpfunc=None) -- stable sort *IN PLACE*; cmpfunc(x, y) -> -1, 0, 1
Alternatively, you could take a look at DSU pattern (Decorate, Sort,
Undecorate):

http://aspn.activestate.com/ASPN/Coo...n/Recipe/52234

--
Ville Vainio http://www.students.tut.fi/~vainio24

[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

[Peter Otten]

Peter Otten wrote:

This is a highly unoptimized version, but at least seems to do the job.

Slightly better:

lst = a.tolist()
lst [[0, 0, 0], [0, 2, 1], [1, 1, 0], [0, 1, 1]] for item in lst: item.reverse() .... lst.sort()
for item in lst: item.reverse() .... lst [[0, 0, 0], [1, 1, 0], [0, 1, 1], [0, 2, 1]]

Peter