Topic: item - list

[amc.dicsac]

Hello such someone could tell me how I know if an item belongs to a list.

Thanks

[ronjonp]

Look into MEMBER or VL-POSITION

[CAB]

And ASSOC

[ur_naz]

What's the fastest one?

[kdub_nz]

What's the fastest one?

Technically they do slightly different things.
Form should follow function, so what do you want returned ??

If you provide a data list and sample code I will check the relative speed of each test for you.

I'm prepared to wager the difference is considerably smaller than the time it takes most people to find a key on the keyboard.

[mailmaverick]

Look into MEMBER or VL-POSITION

I have checked, VL-POSITION is certainly faster than MEMBER.
I am surprised how VL functions are faster than innate functions of LISP which are the basic functions since beginning of LISP.
Can anyone explain the reason.

[Lee Mac]

A difference in memory allocation perhaps? Consider that member returns a list containing the item and all items following it, whereas vl-position merely returns an integer indicating the index of the item.

[mailmaverick]

A difference in memory allocation perhaps? Consider that member returns a list containing the item and all items following it, whereas vl-position merely returns an integer indicating the index of the item.

Indeed.

[snownut2]

Or if an item is a list at all  TYPE

Code - Auto/Visual Lisp: [Select]

1. (setq x '(3))
2.  (=  (Type x) 'LIST)
3.  

[Marc'Antonio Alessi]

Look into MEMBER or VL-POSITION

I have checked, VL-POSITION is certainly faster than MEMBER.
I am surprised how VL functions are faster than innate functions of LISP which are the basic functions since beginning of LISP.
Can anyone explain the reason.

This is an old test:

Code: [Select]

(defun Test_vl-position (InLst)
  (foreach ForElm InLst (vl-position ForElm InLst))
)
(defun Test_member (InLst)
  (foreach ForElm InLst (member ForElm InLst))
)


Code: [Select]

(setq alist1 (atoms-family 1))
(setq alist1 (append alist1 alist1 alist1 alist1))
(timerU '(Test_vl-position alist1) 100)
(timerU '(Test_member      alist1) 100)

TEST_VL-POSITION > 100 iterations: 3.68 secs.
TEST_MEMBER      > 100 iterations: 23.44 secs.


(setq alist1 nil) (setq alist '(1 2 3 4 4 5 5 5 6 7 8 9 9 9 9))
(setq alist1 (repeat 500 (setq alist1 (append alist1 alist))))
(timerU '(Test_vl-position alist1) 100)
(timerU '(Test_member      alist1) 100)

TEST_VL-POSITION > 100 iterations: 0.72 secs.
TEST_MEMBER      > 100 iterations: 1.74 secs.