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newlispfanclub.alh.net • View topic - Intersect bug

Intersect bug

Q&A's, tips, howto's

Intersect bug

Postby tadeas » Tue Mar 04, 2014 8:38 am

tadeas
 
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Re: Intersect bug

Postby cormullion » Tue Mar 04, 2014 10:07 am

Hi tadeas. Is that a bug?
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Re: Intersect bug

Postby tadeas » Tue Mar 04, 2014 10:47 am

tadeas
 
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Re: Intersect bug

Postby cormullion » Tue Mar 04, 2014 11:02 am

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Re: Intersect bug

Postby Lutz » Tue Mar 04, 2014 4:29 pm

When elements in the participating sets are unique, intersect works like the algebraic intersection and the position of sets in the expression is commutative. When not using the true parameter, lists are converted into unique collections sets.

Almost always intersect is used in newLISP to make a selection of elements in one set depending of elements in another set. The positions in the intersect expression are not commutative when elements in a set are not unique. This and the true parameter give us more possibilities selecting elements than using pure algebraic intersection on unique collections.
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Re: Intersect bug

Postby tadeas » Tue Mar 04, 2014 5:30 pm

Very well, this is not a bug.

I made two mistakes:
1) I didn't properly read intersect documentation so I expected it to do something a bit different.
2) I didn't realize that the algebraic intersection doesn't really make sense on lists with the same element more times.

I'm sorry guys.
tadeas
 
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Re: Intersect bug

Postby cormullion » Tue Mar 04, 2014 5:37 pm

No worries - it made me read that part of the manual again, so I gained something too... :)
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Re: Intersect bug

Postby rickyboy » Tue Mar 04, 2014 6:21 pm

What cormullion said. :)

I'm not a beginner at newLISP, and I learned something. Thanks for your post, tadeas!
(λx. x x) (λx. x x)
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