efficient list reduction

[A B Carter]

I have two lists. The values of the second list can be viewed as keys
for the first. I want to create a newlist based on the implied
mapping. The straight Python code would be:

newlist=[]
for key in keys:
newlist.append( oldlist[key])

What's the most efficient way of doing this? The best I could do was
the following list comprehension:

[oldlist[key] for key in keys]

Have I missed something?

Regards, A B Carter

[Carl Banks]

Re: efficient list reduction

A B Carter wrote:[color=blue]
>
>
> I have two lists. The values of the second list can be viewed as keys
> for the first. I want to create a newlist based on the implied
> mapping. The straight Python code would be:
>
> newlist=[]
> for key in keys:
> newlist.append( oldlist[key])
>
> What's the most efficient way of doing this? The best I could do was
> the following list comprehension:
>
> [oldlist[key] for key in keys]
>
> Have I missed something?[/color]


newlist = map(oldlist.__g etitem__,keys)

Quite a bit faster for me.


--
CARL BANKS http://www.aerojockey.com/software
"If you believe in yourself, drink your school, stay on drugs, and
don't do milk, you can get work."
-- Parody of Mr. T from a Robert Smigel Cartoon

[Paul Rubin]

Re: efficient list reduction

gnosticray@aol. com (A B Carter) writes:[color=blue]
> [oldlist[key] for key in keys]
>
> Have I missed something?[/color]

If the keys and values are all characters or small positive ints,
maybe you can contort your program to let you use the very fast
string.translat e operation. Otherwise, use psyco, and if your
listcomp is still not fast enough, write a C extension.