Re: sorting problem
On Apr 2, 1:42 am, Comp1...@yahoo.co.uk wrote:
On Apr 2, 1:35 am, Victor Bazarov <v.Abaza...@comAcast.net> wrote:
Comp1...@yahoo.co.uk wrote:
On Apr 2, 1:10 am, Comp1...@yahoo.co.uk wrote:
Suppose we have pairs of integers of the form (a,b). I
want to define (a,b) <= (c,d) as meaning a >=c and
b<=d (The motivation for this definition is that it means
that the interval (a,b) is a subset of (c,d) ).
Are there any STL functions that can be used for this
type of sort? I don't believe the standard sort (applied
to the standard containers) would work.
I should have said explicitly that I want to sort
according to this new definition of <=. Of course, there
will be incomparable elements. My aim is to transform the
original set of pairs into several sets of pairs where
each set is totally ordered.
Standard sort applies predicate but the predicate should
have the strict weak ordering trait. I am not sure that the
"less-or-equal" qualifies.
The standard requires that pred(a,a) return false. This
definitely means that pred can't be <=.
Yes, I've read that too. But unfortunately my sources are
vague on what "strict weak ordering" means.
I'm not sure that it's an established concept, outside of the
standard. But even if it is, it doesn't really matter---the
standard explicitly defines what it means by the term, and when
the standard explicitly defines a term, that's what it means in
the standard, regardless of what it might mean elsewhere.
Basically, for a binary predicate comp, if we define equiv(a,b)
as !comp(a,b) && !comp(b,a), then both comp and equiv must be
transitive.
Under my ordering, if P and Q are intervals such that neither
P <= Q or Q <= P, it could still hold that P <=Z is true but Q
<= Z is false. I think this property prevents the predicate
being used in sort.
The fact that P <= Q and Q <= P are both true also prevents its
use. (That's what the standard means by "strict".)
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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