sieves

[Ole Schmidt]

Hi,

I have a list: (a b c d e f g h i j k l )
or: (1 2 3 4 5 6 7 8 9 10 11 12)

how can get something for example every third (or n-th) element of my list, like:
(a c f i and so forth...
or: (1 3 6 9...

with length values it must be: (1/8 1/8 1/8 1/8 1/8 1/8 1/8 1/8 1/8 1/8 1/8 1/8)
into: (1/8 -1/8 -1/8 1/8 -1/8 -1/8 1/8 ....

in real life it should be a list of unsorted symbols and length values
a sort xenaxis sieve for already existing material.
Also the ability of mixing the sieves (I think remember that the lisp functions union do not preserve the positions of the elements of the list)

thanks for any hints

ole

[stephane boussuge]

Hi Ole,

this function can help:

(defun collect-every-n (lst strt n)

"collecte dans une liste de symbole lst chaque symbole tout les n en commençant a l'index strt"

  (loop for i from strt to (- (length lst) 1) by n      

        collect (nth i lst)))

;;usage:

;;(collect-every-n '(a b c d e f g h) 0 3)

;;--> (a d g)

cheers

stf

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Stéphane Boussuge

s.bou...@orange.fr

http://algorithmicmusiccomposer.blogspot.fr/

[ole]

that's half way there, thanks!


ole