> Speed-wise, how does referencing a hash table compare with using (assoc x y)
> as I am above. Is it also just hashed values?
For a small case, there's not much difference, but eventually the
hash table wins because it can find the desired element without
searching through a long list.
If you're concerned about speed, it might be faster to use a
vector instead:
(define (entropy-1 string)
(let* ((sum 0.0)
(len (length string))
(top (+ 1 (apply max string)))
(table (make-vector top 0)))
(do ((i 0 (+ i 1))
(element string (cdr element)))
((= i len))
(set! (table (car element)) (+ 1 (table (car element)))))
(do ((i 0 (+ i 1)))
((= i top))
(let ((val (/ (table i) len)))
(if (not (zero? val))
(set! sum (+ sum (* val (log val 2.0)))))))
(- sum)))
> I guess I would prefer hash-table-for-each
I'm leaning that way too. I wanted for-each to work with all
"applicable" types, but currently it doesn't accept hash-tables.
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