On 12/09/2010 05:44 PM, Steven D'Aprano wrote:
(1) Multivariate statistics such as covariance have two obvious APIs:
A pass the X and Y values as two separate iterable arguments, e.g.:
cov([1, 2, 3], [4, 5, 6])
B pass the X and Y values as a single iterable of tuples, e.g.:
cov([(1, 4), (2, 5), (3, 6)]
I currently support both APIs. Do people prefer one, or the other, or
both? If there is a clear preference for one over the other, I may drop
support for the other.
I'm partial to the "B" form (iterable of 2-tuples) -- it
indicates that the two data-sets (x_n and y_n) should be of the
same length and paired. The "A" form leaves this less obvious
that len(param1) should equal len(param2).
I haven't poked at your code sufficiently to determine whether
all the functions within can handle streamed data, or whether
they keep the entire dataset internally, but handing off an
iterable-of-pairs tends to be a little more straight-forward:
cov(humongous_dataset_iter)
or
cov(izip(humongous_dataset_iter1, humongous_dataset_iter2))
The "A" form makes doing this a little less obvious than the "B"
form.
(2) Statistics text books often give formulae in terms of sums and
differences such as
Sxx = n*Σ(x**2) - (Σx)**2
There are quite a few of these: I count at least six common ones,
When you take this count, is it across multiple text-books, or
are they common in just a small sampling of texts? (I confess
it's been a decade and a half since I last suffered a stats class)
all closely related and confusing named:
Sxx, Syy, Sxy, SSx, SSy, SPxy
(the x and y should all be subscript).
Are they useful, or would they just add unnecessary complexity?
I think it depends on your audience: amateur statisticians or
pros? I suspect that pros wouldn't blink at the distinctions
while weekenders like myself would get a little bleary-eyed
without at least a module docstring to clearly spell out the
distinctions and the forumlae used for determining them.
Just my from-the-hip thoughts for whatever little they may be worth.
-tkc
--
http://mail.python.org/mailman/listinfo/python-list
