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https://issues.apache.org/jira/browse/NUMBERS-215?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18117065#comment-18117065
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Gilles Sadowski commented on NUMBERS-215:
-----------------------------------------
bq. [...] still an instance method [...]
Yes, because it's contains a "vararg"; to make it {{static}}, one has to pass
{{k}}, but that argument must come before the "vararg" one; and this would
entail a slightly inconsistent API:
{code}
of(int n, int k)
{code}
vs
{code}
stream(int k, T... items)
{code}
Since the "vararg" is syntactic sugar for when the application developer
explicitly expands the sequence of items, I think that there is no harm in
having to write
{code}
List<List<String>> all = Stirling.S2.of(4, 2).stream("A", "B", "C", "D")
.collect(Collectors.toList());
{code}
The alternative would be to remove the "vararg" version.
We could provide the array version:
{code}
stream(T[] items, int k)
{code}
so that the developer could write
{code}
List<List<String>> all = Stirling.S2.stream(new String[] {"A", "B", "C", "D"},
2)
.collect(Collectors.toList());
{code}
But that becomes longer than the original version!
Moreover, the redundancy of passing (explicitly) {{n}} to {{of(n, k)}} and
(implicitly) to {{stream}} might useful in early detection of a programming
error (e.g. where the same {{S2}} instance would be used to iterate over
different list of items that are assumed to have the same size).
> Stirling partitions generator
> -----------------------------
>
> Key: NUMBERS-215
> URL: https://issues.apache.org/jira/browse/NUMBERS-215
> Project: Commons Numbers
> Issue Type: New Feature
> Components: combinatorics
> Reporter: Gilles Sadowski
> Assignee: Gilles Sadowski
> Priority: Minor
> Fix For: 1.4
>
>
> Would it be useful to provide functionality to *iterate* over the partitions
> defined by "Stirling number of the second kind" (i.e. all partitions into K
> subsets, of a set of N elements)?
> Code would be in a nested static class of the existing
> [{{Stirling}}|https://commons.apache.org/proper/commons-numbers/commons-numbers-combinatorics/apidocs/src-html/org/apache/commons/numbers/combinatorics/Stirling.html]
> class:
> {code}
> public final class Stirling {
> // ...
> public static final class S2 implements Iterable<List<List<Integer>> {
> // ...
> public static S2 of(int n, int k) {
> // ...
> }
> }
> }
> {code}
> I have a potential use case (for very small "N").
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