<div class="gmail_quote">On Wed, Sep 9, 2009 at 4:37 PM, Doug Williams <<a href="mailto:m.douglas.williams@gmail.com">m.douglas.williams@gmail.com</a>> wrote: <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> Thanks for running them for me. I guess it comes down to whether the flexibility is worth the performance hit. I like the flexibility. In the past there were times I have had to convert lists to vectors just to compute statistics on them, which is even less efficient. I could include the old ones as vector-mean, vector-variance, etc for people who need/want the performance. Doug<div><div></div> </div></blockquote><div> Why not special case for vectors instead of adding to the module interface? </div></div> (define (mean data) (if (vector? data) (vector-mean data) (generic-mean data)) (define (generic-mean data) (for/fold ((m-old 0.0)) ((i (in-naturals)) (x data)) (+ m-old (/ (- x m-old) (add1 i))))) <pre>(define (vector-mean data) (let ((n (vector-length data)) (mu 0.0)) (do ((i 0 (+ i 1))) ((= i n) mu) (set! mu (+ mu (/ (- (vector-ref data i) mu) (+ i 1))))))) </pre>-- Marco