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fastest way to merge lists.

Hrvoje Niksic hniksic at iskon.hr
Sat Jan 8 22:19:37 EST 2000 
Roy Smith <roy at popmail.med.nyu.edu> writes:

> I'm not yet sure if care if the final list is sorted or not.  For
> now, I think it doesn't matter.  What's the fastest way to do that?
> It seems to me:
> 
> d = {}
> for s in list1:
>    d[s] = 1
> for s in list2:
>    d[s] = 1
> for s in list3:
>    d[s] = 1
> for s in list4:
>    d[s] = 1
> for s in list5:
>    d[s] = 1
> list = d.keys()
> del d   # if I care about memory
> 
> would be pretty good.  Anything better?

How about:

# cat
biglist = list1 + list2 + list3 + list4 + list5
# sort
biglist.sort()
# uniq
index = 0
while index < len(biglist) - 1:
  if biglist[index] == biglist[index + 1]:
    del biglist[index]
  else:
    index = index + 1

I haven't compared this solution with yours, but note that it's
directly equivalent to Unix-ese `cat | sort | uniq'.
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