Sage operations that preserve order

[tvn]

Does Sage has some data structure like set that preserve the order of the elements ?  For example ,  I want set([1,2,3,1) to always return 1,2,3 .  In addition to set(), I also need operations of set like difference, intersection ,etc that guarantees some specific orders.   Thanks,  

[Jason Grout]

set is a python datatype, so one thing to do is look for 'python ordered
set'. Indeed, one of the first links was a stack overflow question that
pointed to this:

http://code.activestate.com/recipes/576694/

Thanks,

Jason

[William Stein]

If you just care about order when iterating, use sorted:

for x in sorted(set([1,2,3,1])):
print x

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William Stein
Professor of Mathematics
University of Washington
http://wstein.org