Fastest way to max() list

[Chris Rebert]

On Thu, Sep 25, 2008 at 8:57 PM, David Di Biase <dave.dibiase at gmail.com> wrote:
> I have a list with about 1000-1500 sub-lists which look like so:
> list[-0.28817955213290786, 3.6693631467403929, 'H', 31.31225233035784]]
>
> The first and second values are Angstrom units specifying the location of a
> particle. What I'd like to do is determine the distance between the smallest
> and largest value in the arrays first position 0. I tried reading the manual
> for this but I don't see how it applies key or any of those other commands
> to the function. I could easily write a sort to do this and capture the
> first and last spots, but why do that when I can use max and min (if I can
> actually do that...).

A. You should probably be using objects rather than arrays to
represent your datapoints, so that they're more structured and it's
more apparent what the values mean.

B. Assuming by "distance" you meant "difference" and/or that the
distance is only in 1 dimension:

from operator import itemgetter
firsts = map(itemgetter(0), main_list)
distance = max(firsts) - min(firsts)

>
> So you wonderful Python gods, lay some knowledge on me. please? lol...
>
> while I'm at it, is there a way to modify an entire list without having to
> produce a whole new one? For example now say I want to modify list[0] and
> multiply it by some value. From what I understand previous version of Python
> allowed lists to be multiplied like matrices...now apparently it just
> replicates the list. :-/ shucks...

You just have to apply the transform to each list element individually
(also, you might consider using NumPy [http://numpy.scipy.org/] if
you're doing a lot of matrix manipulation):

for lst in main_list:
    lst[0] *= some_value

Regards,
Chris

>
> The first question would be useful to know, but the second question I do
> quite a bit of and the "best practice" would be really great to know!
>
> Thanks in advanced!
>
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