> [...]
>
> 1) do nothing to check the array is the same between calls and blindly
> assumes it IS the same. Users would really need to call clearCache
> when they provide a new array
> pros: very simple
> cons: error-prone for the user as it relies only on reading and
> understanding a documentation that would change with new version
>
> 2) check only array reference equality (with ==) to check the array
> is the same as the previous call or not. Users would need to call
> clearCache only if they use the same array but have changed its
> content.
> pros: trade-off between efficiency and reliability,
> handles most cases properly
> cons: may be wrong in corner cases
>
> 3) check array content using an hash code. Users would generally don't
> need to call clearCache at all so it would not be provided
> pros: works in all cases
> cons: add linear cost for array checking
>
> 4) remove the double[] values parameter from the API and use a separate
> addValues method, hence the class will reset its cache only when
> addValues is called
> pros: works in all cases
> cons: Percentile could not implement UnivariateStatistic anymore
>
> My preference is choice 2.
>
> What do you think ?
IIUC, the interface method ("evaluate") was designed around the assumption
that successive calls are independent: the array argument is not
encapsulated for further processing (e.g. caching).
IMO, the equality check and the "clearCache" method look like workarounds,
not a clean solution.
As an example, what if a user calls "evaluate" several times alternating on
two different arrays:
---CUT---
double[] a = new double[] {1, 2, 3};
double[] b = new double[] {1, 2, 3, 4, 5};
Percentile p = new Percentile();
dourble r;
r = p.evaluate(a, 50);
r = p.evaluate(b, 50);
r = p.evaluate(a, 50);
r = p.evaluate(b, 50);
// etc.
---CUT---
Doesn't this kind of use-case nullify the expected optimization?
If the array is going to be reused, the user call should reflect that fact;
e.g. by passing the array in a constructor:
---CUT---
double[] a = new double[] {1, 2, 3};
double[] b = new double[] {1, 2, 3, 4, 5};
Percentile pA = new Percentile(a);
Percentile pB = new Percentile(b);
double r;
r = pA.evaluate(50);
r = pB.evaluate(50);
r = pA.evaluate(50);
r = pB.evaluate(50);
---CUT---
That way, later calls can benefit from whatever preprocessing was done in
previous calls.
The instance will always control all the information needed (e.g. after a
call to an "addValues" method) for the processing without the need to rely
on the user for calling "clearCache" whenever necessary.
Gilles
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