Extracting (efficiently) a sub-list from a list

[jbreard]

Good morning (evening) everyone,

 

I have a question which will seam basic to you I guess concerning a simple list manipulation.

 

I have a list of the form ((X0 Y0 Z0 T0)  (X1 Y1 Z1 T1)...(Xn Yn Zn Tn)) and I want to extract efficiently a sublist form this list ((Xi Yi Zi Ti)....(Xj Yj Zj Tj)) given that I know the ranges i and j.

 

I know how to do that using a "while" loop and populating a sublist by accessing the elements trough "nth" but that is not very efficient. An other approch could alos be to use a formula using 2 time "member" and "reverse" and "nth" but that is not efficient as well.

 

I have to perform this extraction on a list whose length is about 40 000 and I must perform this extraction about 2000 times. Hence the need for speed...

 

I'm sure that a language like AutoLISP must have efficient ways to do that but I don't see it at the moment.

 

Does anyone as an insight on that matter ? Maybe a basic function that I don't know about ?

 

Thank you very much for your help,

 

Jacques

[rlx]

http://www.lee-mac.com/sublist.html

[jbreard]

Thanks a lot,

 

That is just perfect. I know of course of Lee-Mac's treasure's website but I missed this one

 

Have a nice day,

 

Jacques