I've been working on a Java 8 wrapper class around double[] in my day
job, and added the following factory method:
/**
* Obtains an instance with entries filled using a function.
* <p>
* The function is passed the array index and returns the value for
that index.
*
* @param size the number of elements
* @param valueFunction the function used to populate the value
* @return an array initialized using the function
*/
public static DoubleMatrix1D of(int size, IntToDoubleFunction valueFunction) {
if (size == 0) {
return EMPTY;
}
double[] array = new double[size];
for (int i = 0; i < array.length; i++) {
array[i] = valueFunction.applyAsDouble(i);
}
return new DoubleMatrix1D(array);
}
View on GitHub here:
https://github.com/OpenGamma/Strata/commit/63e73652194a3dd94e37fbc407f4933c10abadda#diff-2a9787868cf0654b4a6a07e75c1a6286R199
It occurs to me that it would be a *very* good idea to add a similar
method to List.
public static <T> List of(int size, IntFunction<T> valueFunction) { ... }
Stephen
On 14 October 2015 at 11:39, Stephen Colebourne <[email protected]> wrote:
> On 14 October 2015 at 10:38, Paul Sandoz <[email protected]> wrote:
>>> On 14 Oct 2015, at 06:18, Stuart Marks <[email protected]> wrote:
>>> I'm not entirely sure what to take from this. If it were clearly
>>> exponential, we could say with confidence that above a certain threshold
>>> there would be vanishingly little benefit adding more arguments. But since
>>> the curve seems to flatten out, maybe this is pushing us to add more pairs
>>> than we had originally thought. The current draft API has 8 pairs; that
>>> seems to leave a few percent of cases on the table. Obviously we can't get
>>> to 100%, but is 97% good enough?
>
> I'd say 5 is definitely too little, without an easy builder fallback
> (as Guava provides). I'd say the right number is between 8 and 10.
>
> Stephen
