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Re: how to access a large datastructure efficiently?
From: |
Christian Wittern |
Subject: |
Re: how to access a large datastructure efficiently? |
Date: |
Thu, 4 Mar 2010 08:15:47 +0000 (UTC) |
User-agent: |
Loom/3.14 (http://gmane.org/) |
Thierry Volpiatto <thierry.volpiatto <at> gmail.com> writes:
> >> I have a large list of items which I want to access. The items are in
> >> sequential order, but many are missing in between, like:
> >>
> >> (1 8 17 23 25 34 45 47 50) [in reality, there is a value associated
> >> with this, but I took it out for simplicity]
>
> ,----
> | (defun closest-elm-in-seq (n seq)
> | (let ((pair (loop with elm = n with last-elm
> | for i in seq
> | if (eq i elm) return (list i)
> | else if (and last-elm (< last-elm elm) (> i elm)) return
(list last-elm i)
> | do (setq last-elm i))))
> | (if (> (length pair) 1)
> | (if (< (- n (car pair)) (- (cadr pair) n))
> | (car pair) (cadr pair))
> | (car pair))))
> `----
> For the smallest just return the car...
>
This seems to do what I need, thanks! Now I have to see how that
performs on the real data. I was hoping there would be a method
that did not involve loops, but some kind of binary search. Would it be
possible to use a hash-table here?
Christian