To guard against NPEs, align-to-tick-size should be
(defn align-to-tick-size
[tick-map value]
(if-let [tick-size (get-tick-size tick-map value false)]
(let [remainder (mod value tick-size)]
(if (zero? remainder)
value
(* tick-size ((if (>= remainder (/ tick-size 2)) inc identity)
(quot value tick-size)))))
value))
On Jan 23, 11:18 am, Eugen Dück <[email protected]> wrote:
> Anyone who has seen the subject implemented in Java/Swing might have
> been stunned by the hundreds of lines of code that were deemed
> necessary for it, with their appropriate share of bugs. (And an
> implementation I've seen in C#/NetAdvantage was even worse, which was
> less related to the language itself, as to the GUI toolkit)
>
> I knew this could be done way more elegant, but I was surprised it can
> be done THIS nicely - if done in clojure. And if you think this can be
> improved further or find any bugs, shoot!
>
> Example: Prices for Japanese stock have a step size of
> 1 in the interval [0,3000],
> 5 in the interval (3000,5000],
> ...
>
> An easy way to model that would be a sorted map:
>
> (def japanese-stock-tick-map
> (sorted-map
> 0 1
> 3000 5
> 5000 10
> 30000 50
> 50000 100
> 300000 500
> 500000 1000
> 3000000 5000
> 5000000 10000
> 30000000 50000
> 50000000 100000))
>
> Figuring out the step size - which on the interval edges depends on
> whether you go up or down - can be done like this:
>
> (defn get-tick-size
> [tick-map value go-up?]
> (second (first (rsubseq tick-map (if go-up? <= <) value))))
>
> Aligning an arbitrary value to the closest valid number (if
> necessary):
>
> (defn align-to-tick-size
> [tick-map value]
> (let [tick-size (get-tick-size tick-map value false)
> remainder (mod value tick-size)]
> (if (zero? remainder)
> value
> (* tick-size ((if (>= remainder (/ tick-size 2)) inc identity)
> (quot value tick-size))))))
>
> Now implementing the SpinnerModel is trivial (which is why I will not
> copy it here, but leave it onhttp://dueck.org/tick/tick-size-spinner.html
> in a simple demo for anyone to try out).
>
> You're the man, Rich!
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