Let f be a function {1,2,3,...,n} -> C. What is the most elegant way to restrict this function to an arbitrary subset of {1,2,3,...,n}?
In other words I would like to have an operator R which takes such a function f and a subset S of [n] and returns a function f': S -> C which coincides with f on S.
I am not sure whether it is elegant but you can do it in a straightforward way:
sage: def R(f,S):
....: def f_restricted(s):
....: if s in S:
....: return f(s)
....: else:
....: raise ValueError, 'Element not in the set'
....: return f_restricted
....:
sage: g = R(lambda x : 3*x, [1,2,3])
sage: g(2)
6
sage: g(5)
ValueError: Element not in the set
You can also make R a Python decorator.
OK, thanks. Since the idea is a generalization of python/itertools/islice I thought it might be possible that it was build into some basic data structure or utility of Sage. The idea of a decorator is interesting.
Asked: 2016-10-08 14:19:51 +0100
Seen: 940 times
Last updated: Oct 08 '16
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