set-theory

Given this table structure and example data (t3 should not be used in the query, it is only here to show the relation between t1 and t2): t1 t2 t3 -------------- ----------------- -------------------------------- | id | value | | t1key | t3key | | id | value | | 1 | 2008 | | 3 | 1 | | 1 | "New intel cpu in 2010" | | 2 | 2009 | | 4 | 1 | | 2 | "New amd cpu in 2008" | | 3 | 2010 | | 6 | 1 | | | ... | | 4 | intel | | 1 | 2 | -------------------------------- | 5 | amd | | 5 | 2 | | 6 | cpu | | 6 | 2 | | | ... | | | ... | -------------- ----------------- How would you build a SQL query that would

I have a large number of sets of numbers. Each set contains 10 numbers and I need to remove all sets that have 5 or more number (unordered) matches with any other set. For example: set 1: {12,14,222,998,1,89,43,22,7654,23} set 2: {44,23,64,76,987,3,2345,443,431,88} set 3: {998,22,7654,345,112,32,89,9842,31,23} Given the 3 sets of 10 numbers above sets 1 and sets 3 would be considered duplicates because they have 5 matching numbers. So, in this case I would remove set 3 (because it's considered similar to set 1). I have over 10000 sets to compare and I want to do this very efficiently. I've

consider the following script: # multipleSmallFrozensets is a list of 7 frozensets of differenet number of string objects multipleSmallFrozensets = [ frozenset({'YHR007C', 'YHR042W'}), frozenset({'YPL274W'}), frozenset({'YCL064C'}), frozenset({'YBR166C'}), frozenset({'YEL041W', 'YJR049C'}), frozenset({'YGL142C'}), frozenset({'YJL134W', 'YKR053C'})] # singleFrozenset is a frozenset of 3410 string objects singleFrozenset = frozenset({'YIL140W','YLR268W','YLR357W','YJL155C','YHR067W', 'YAL008W','YBR255W','YFR027W','YGR148C','YJR122W','YJL204C','YJL093C','YLR244C', 'YNL003C','YBR111W-A', ...}) #

I'm making a password brute forcing tool as a learning exercise, and I want it to be resumable. So, what I want is to be able to say, this is the set of possible characters, if I computed the Cartesian set of every possible combination of this set up to length n, what is the set at point x? However, I want to do this without computing the entire set. I've seen similar logic in one place online but I was unable to generalise this to fit. Any help would be fantastic, thanks! I'm fluent in C# if that helps. Edit: Here's the question I mentioned earlier: How to select specific item from cartesian

I am trying to implement a list difference routine in prolog. For some reason the following fails: difference(Xs,Ys,D) :- difference(Xs,Ys,[],D). difference([],_,A,D) :- D is A, !. difference([X|Xs],Ys,A,D) :- not(member(X,Ys)), A1 is [X|A], difference(Xs,Ys,A1,D). When trying: ?- difference([1,2],[],D). I get this error: ERROR: '.'/2: Type error: `[]' expected, found `1' ("x" must hold one character) ^ Exception: (10) _L161 is [2|1] ? Your usage A1 is [X|A] is incorrect. Predicate is is used only for arithmetics. Btw, SWI-Prolog has built-in subtract predicate: 1 ?- subtract([1,2,3,a,b],[2,a]

I have two collections a and b . I would like to compute the set of items in either a or b , but not in both (a logical exclusive or). With LINQ, I can come up with this: IEnumerable<T> Delta<T>(IEnumerable<T> a, IEnumerable<T> b) { return a.Except (b).Union (b.Except (a)); } I wonder if there are other more efficient or more compact ways of producing the difference between the two collections. Edit 1: Jon Skeet posted a first solution which does not preserve the order of the items by relying on a HashSet . I wonder if there are other approaches which would preserve the order of a and b in the