Chaining Interval Operations

[geographika]

Very nice library - thanks!

I was wondering if you have a suggested method for chaining interval operations on lists of intervals?

For example for intersecting several lists you can use:

r = P.closed(100.1239812, 300.9012312) | P.closed(110, 300.9012312) | P.closed(97, 300.9012312)

If you have a list of unknown size is it possible to chain the intersection?

It would be nice if one of the approaches for chaining sets could be used as described here:

>> list(set.union(*map(set, a)))
[1, '44', '30', '42', '43', '40', '41', '34']

>>> from itertools import chain
>>> list(set(chain.from_iterable(d)))

So something like:

>>> from itertools import chain
>>> list(P.intersection(chain.from_iterable(d)))

Maybe this is already possible but I've not found a successful approach so far (beyond a simple loop and applying intersection one by one).

[AlexandreDecan]

Hello,

I'm not 100% sure I understood the question, but if I'm right, what you're looking for is reduce from the functools module (see https://docs.python.org/3/library/functools.html#functools.reduce). The function will be P.Interval.intersection, the iterable will be the list of intervals, and the initializer will be the infinite interval (i.e. P.open(-P.inf, P.inf)).

For example:

>>> import portion as P
>>> m = [P.closed(0, 10), P.closed(2, 8), P.closed(1, 4)]
>>> from functools import reduce
>>> reduce(P.Interval.intersection, m, P.open(-P.inf, P.inf))
[2, 4]

Is it what you were looking for?

[geographika]

@AlexandreDecan - yes exactly that. I was didn't realise P.Interval.intersection was a class method and hadn't thought of using P.open(-P.inf, P.inf) as the starting point.
Thanks!

[AlexandreDecan]

You're welcome ;-)

Note that P.Interval.intersection is not a class method but, thanks to Python, if a is an instance of class A, then a.f() is (nearly) equivalent to A.f(a), so we can use instance methods as class methods :-)

[geographika]

Thanks for the further explanation.

For anyone who comes across this issue and needs to chain a union using P.empty() as follows allows a chained operation:

from functools import reduce
m = [P.closed(0, 10), P.closed(2, 8), P.closed(1, 4)]
reduce(P.Interval.union, m, P.empty())
>>> [0,10]