Remove item from list

I got the right result by using [b] copy [/b] and [b] remd [/b]

A='(0 1 2 3 4 5 6 7 8 9)
B='(1 3 5 7 9)
C=copy(A)
foreach(item A
if(member(item B) then
remd(item C)
)
)

Hi Leon,

remove is a destructive function so you were correct to use copy.
Another (faster) method is to use cons, to create a new list, or the slowish following method
C = setof(item, A, !member(item, B))

Cheers, Dave

Thanks Dave,
I havn't think of !member,
At first, I used member(item B)=nil, it doesn't work. Haha~~

below is what I use, it is very fast and does not go through unnecessary loops if you have duplicates in list A (or if all items in A have already been removed)

A='(1 2 1 3 1 4 1 5)
B='(1 3 5)

procedure(SubstractList(B A)
let((item)
while(B && A
item=car(B)
B=cdr(B)
A=remove(item A)
)
A
)
)

Note that both lists are modified inside the procedure. This is ok since they are copies.
If both lists are dbids, then creating another procedure that uses "req" instead of "remove" will be even faster.