changing sign (+/-) in lists and/or angle between 2 vectors

Hi all,

I am pretty new to both Rhino and GH. (started 3 days ago) Everything was breezy until I got stuck with this problem.

1. I have set of numbers in my list. (e.g. {a1, a2, a3, a4, a5, a6, ..., a1200)}) Is there any way I can make this list into {a1, a2, a3, a4, -a5, -a6, -a7, -a8, a9, a10, a11, a12, -a13, ..... , a1200} ? ( 4 positive signs then 4 negative signs and so on) - alternating every nth in general.

2. Is there any way (workaround) to get negative angle value from 2 vectors? I know 'ANGLE (of 2 vectors)' component by itself doesn't work and I know why too. I have feeling that the reflex angle output might be useful but again, matter of list manipulation.

Any help would be greatly appreciated. Thanks in advance.

Hyo

Replies to This Discussion

Permalink Reply by Victor Leung on April 3, 2010 at 2:29pm

I dont have GH at hand, but by the mean time while no replies appear, you can try this,

If it is just a list of items, i assume it is a floating number, you can split the list according to a pattern : TTTTFFFF, so it splits the list into two. One of the output you do a mathmetical operation which turns it to negative (eg: use a function 0-x or use a subtract operator) then weave the two list back using a similar pattern, TTTTFFFF.

I'm not sure if this works or now, otherwise you can try using tree structure, which is more coplicated for me.

cheers
Victor

Permalink Reply by Hyo Hwang on April 3, 2010 at 8:18pm

Thanks a lot for the input, Victor.

I looked at the 'list' and 'tree' part closely again following your suggestion. I had no knowledge on culling and weaving 'patterns'.

After figuring out the logic with a hard coded true/false list (picture #1), I created the true/false stream that is controlled by parameters in my drawings. (picture #2) In my project, the 'int' stream and 'repetition' information can be feed parametrically.

I sill have feeling that my solution is too complicated. Please help me improve (simplify) this. Anyone?

Hyo

Attachments:

culling01.jpg, 168 KB
culling02.jpg, 211 KB

Permalink Reply by trevor.patt on April 4, 2010 at 4:56am

Try this.
"Floor (x/y)" gives you a list of integers repeated (in this case) 4 times: 0,0,0,0,1,1,1,1,2,2,2,2...
"_ mod 2" turns that list into 0 and 1: 0,0,0,0,1,1,1,1,0,0,0,0...
"_ -.5) *2" changes that list to 1 and -1: 1,1,1,1,-1,-1,-1,-1,1,1,1,1...

Do definitely look more closely at lists, treas, cull, weave, etc. though. They are the solutions to 65% of GH problems.

Attachments:

changing signs.jpg, 126 KB

Permalink Reply by Hyo Hwang on April 4, 2010 at 11:43pm

Wow, this is really nice!

so the 'floor' being... that of 'floor and ceiling' function? Very creative. I am definitely going to use this.

Thanks a lot!

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