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Re: bike shifting - output decimal in percent


From: Tomas Nordin
Subject: Re: bike shifting - output decimal in percent
Date: Sun, 19 May 2019 09:53:35 +0200

Emanuel Berg <address@hidden> writes:

>>> (format "%2.2g%%" (* 100.0 foo)) => "31%"
>>
>> Great, thanks a lot :)
>
> Oups, spoke (no pun intended :)) too soon.
> Too much respect for Drew, I suppose ;)
>
> But to be honest, the original program is
> _much_ better. Check out the examples below:
>
> ;; secret bonus program :)
> ;; thanks to friend at #emacs
> (defun percent-string (decimal)
>   (concat
>    (number-to-string
>     (round (* 100 decimal)) ) "%") )
> ;; test: (percent-string 0.42857142857142855) ; "43%"
>
> (defun bike-compute-step (from to)
>   (percent-string
>    (/ (- from to)
>       from
>       1.0) ))
> ;; test - should be 43% for
> ;; one 42t and one 24t chainring
> ;; according to an article in the spring 2019 issue
> ;; of "Bicycle Quarterly" (ISSN 1941-8809) -
> ;; (bike-compute-step 42 24) ; "43%"
>
> ;; (percent-string 0.01)  ; "1%"
> ;; (percent-string 0.1)   ; "10%"
> ;; (percent-string 1)     ; "100%
> ;; (percent-string 2)     ; "200%"
>
> ;; (format "%2.2g%%" (* 100.0 0.01)) ; " 1%"    (?)
> ;; (format "%2.2g%%" (* 100.0 0.1))  ; "10%"
> ;; (format "%2.2g%%" (* 100.0 1))    ; "1e+02%" (!?)
> ;; (format "%2.2g%%" (* 100.0 2))    ; "2e+02%" (...)

Why not just use good old %f?

(format "%.0f%%" (* 0.127 100)) ;; -> "13%"

Or respecting SI recommendations:

(format "%.0f %%" (* 0.127 100)) ;; -> "13 %"



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