#20057: Add iterator to DisjointSet class
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Reporter: jmantysalo | Owner:
Type: enhancement | Status: needs_info
Priority: major | Milestone: sage-7.1
Component: combinatorics | Resolution:
Keywords: | Merged in:
Authors: Jori Mäntysalo | Reviewers: Travis Scrimshaw
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/jmantysalo/iterate_disjoint_set | 1f96bc01bd77eea0bd64613a97c3f41857789526
Dependencies: | Stopgaps:
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Comment (by jmantysalo):
I want to make a function computing congruence of a (finite) lattice
generated by some element sets. The result is splitting of elements to
sets, i.e. exactly disjoint union. Hence `DisjointUnion` feels natural
choise. The code basically iterates "elements `a` and `b` must belong to
same equivalnce class, so combine set containing `a` and set containing
`b`."
If I understood right, there is no way to make a fast iteration of values
possible; the whole idea of this data structure is to avoid moving data in
memory so that iterating would become fast.
I think that `itervalues()` and not `iterkeys()` is the right solution, if
we are going to make this. There is basically no "roots" in mathematical
sense in disjoint union. So the question is about "expected to be
efficient". I would vote against it: we can make a slow iterator.
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Ticket URL: <http://trac.sagemath.org/ticket/20057#comment:7>
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