[Tutor] Efficiency and speed

[James Reynolds]

On Sat, Mar 20, 2010 at 1:17 PM, Steven D'Aprano <steve at pearwood.info>wrote:

> On Sat, 20 Mar 2010 05:47:45 am James Reynolds wrote:
>
> > This is a monte-carlo simulation.
> >
> > The simulation measures the expiration of something and those
> > somethings fall into bins that are not evenly dispersed. These bins
> > are stored in the nx list mentioned previously.
> >
> > So let's say you have the bins, a, b,c,d,e,f and you have the value z
> > from the sample list where z >b and <= a. In this case, it should
> > return the index value at position (a).
>
> I'm not sure I understand completely. An example might help. I *think*
> you have a list like this:
>
> nx = [10.0, 9.0, 7.0, 3.0, 2.0, 1.0]
>
> and if you have a value like z = 9.8 you want to return the index 0.
> Correct?
>
> That seems a bit funny. In my experience it is normal to have the bins
> in the opposite direction. I suppose it probably doesn't matter that
> much, but it does seem a bit unusual.
>
> If nx is fairly short (say, less than 40 or 50 items), then the fastest
> way is probably a linear search, something like this:
>
> def search_bins(nx, z):
>    """Search bins nx for item z.
>
>    >>> bins = [5.0, 4.0, 2.0, 1.0]
>    >>> search_bins(bins, 1.2)
>    2
>
>    If z is not in the bins, returns -1:
>
>    >>> search_bins(bins, 5.1)
>    -1
>
>    """
>    for i, value in enumerate(nx):
>        if z > value:
>            return i-1
>    return -1
>
>
>
>
> --
> Steven D'Aprano
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Firstly,

Thank you to everyone who responded to this thread. I learned some very
important lessons, some of which I've been working on over the weekend. I
apologize for not responding sooner.

I tinkered around with the aforementioned algorithm and I ended up using the
bisect that Emilie showed earlier. I did end up making the nested for loop
work earlier using an if statement, but the bisect was much more efficient
(.24 seconds running 100K trials), which is a major improvement. I've just
started using profiler this weekend, and It's giving me some incite into how
the language functions.

On that end, I'm almost done readying "beginning Python: From Novice to
Professional" Can anyone recommend anything else for me to read after that?
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