On Wed, Apr 24, 2013 at 4:11 AM, Sebastian Berg <sebastian@sipsolutions.net> wrote:
On Tue, 2013-04-23 at 23:33 -0400, josef.pktd@gmail.com wrote:
On Tue, Apr 23, 2013 at 6:16 PM, Sebastian Berg <sebastian@sipsolutions.net> wrote:
On Tue, 2013-04-23 at 12:13 -0500, Jonathan Helmus wrote:
Back in December it was pointed out on the scipy-user list[1] that numpy has a percentile function which has similar functionality to scipy's stats.scoreatpercentile. I've been trying to harmonize these two functions into a single version which has the features of both. Scipy PR 374[2] introduced a version which look the parameters from both the scipy and numpy percentile function and was accepted into Scipy with the plan that it would be depreciated when a similar function was introduced into Numpy. Then I moved to enhancing the Numpy version with Pull Request 2970 [3]. With some input from Sebastian Berg the percentile function was rewritten with further vectorization, but neither of us felt fully comfortable with the final product. Can someone look at implementation in the PR and suggest what should be done from here?
Thanks! For me the main question is the vectorized usage when both haystack (`a`) and needle (`q`) are vectorized. What I mean is for:
np.percentile(np.random.randn(n1, n2, N), [25., 50., 75.], axis=-1)
I would probably expect an output shape of (n1, n2, 3), but currently you will get the needle dimensions first, because it is roughly the same as
[np.percentile(np.random.randn(n1, n2, N), q, axis=-1) for q in [25., 50., 75.]]
so for the (probably rare) vectorization of both `a` and `q`, would it be preferable to do some kind of long term behaviour change, or just put the dimensions in `q` first, which should be compatible to the current list?
I don't have much of a preference either way, but I'm glad this is going into numpy. We can work with it either way.
In stats, the most common case will be axis=0, and then the two are the same, aren't they?
What I like about the second version is unrolling (with 2 or 3 quantiles), which I think will work
u, l = np.random.randn(2,5) or res = np.percentile(...) func(*res)
The first case will be nicer when there are lots of percentiles, but I guess I won't need it much except for axis=0.
Actually, I would prefer the second version, because it might be a bit more cumbersome to get the individual percentiles out if the axis is somewhere in the middle, however I don't think I have a case like that.
I never thought about the axis being where to insert the dimensions of the quantiles. That would be a third option. It feels simpler to me to just always use the end (or the start) though.
If the choices are start or end, then I prefer start for unpacking. Josef
- Sebastian
The first version would be consistent with reduceat, and that would be more numpythonic. I would go for that in numpy.
my 2.5c
Josef
Regards,
Sebastian
Cheers,
- Jonathan Helmus
[1] http://thread.gmane.org/gmane.comp.python.scientific.user/33331 [2] https://github.com/scipy/scipy/pull/374 [3] https://github.com/numpy/numpy/pull/2970 _______________________________________________ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
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