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http://issues.apache.org/jira/browse/LANG-238?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12461664
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Simon Kitching commented on LANG-238:
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I would agree with Stephen that an "allEquals(a)" method isn't likely to be
widely used. And besides, it can be implemented for non-floating-point as:
Set<integer> aSet = new HashSet<Integer>(Arrays.asList(a));
boolean allEq = (aSet.size() <= 1);
which doesn't seem to me sufficiently complicated to deserve inclusion in lang.
A "containsOnly(a,b)" method would be more generally useful but can be
implemented as:
Set<Integer> aSet = new HashSet<Integer>(Arrays.asList(a));
Set<Integer> bSet = new HashSet<Integer>(Arrays.asList(b));
// or if b has one element, bSet = Collections.singleton(val);
boolean contained = bSet.containsAll(aSet);
which again doesn't seem terribly complicated.
However if a more generic method is being considered, then how about:
T[] notIn(T[] a, T[] b);
which returns the elements in a that are not in b? I'm not a mathematician but
I believe this is written in set operations as "a - b", or in words as "the
complement of a with respect to b", so this method could also be called:
T[] subtract(T[] a, T[] b);
or
T[] complement(T[] a, T[] b);
though I think "notIn" is more obvious for most users.
Actually, this operation is the array equivalent of Collections.removeAll, so
that's an alternative name:
T[] removeAll(T[] a, T[] b);
The test "allEquals(a, b)" is then:
boolean allEq = NumberUtils.notIn(a, b).length == 0;
and the test "allEquals(a)" is:
boolean allEq = NumberUtils.notIn(a, new Integer[] {a[0]}).length == 0;
BTW, the "a" parameter is really an array representation of a bag, not a set so
maybe this set terminology could be misleading.
If such a set/bag operation is provided, then intersection and union could also
reasonably be provided for arrays:
T[] intersection(T[] a, T[] b);
T[] union(T[] a, T[] b);
Not sure whether union should treat its params as bags (in which case union
would be equivalent to concat) or sets (only one occurrence for elements in
both a and b).
At this point, this appears to be bordering on commons-collections or
commons-math functionality but as this is only for arrays I think a good
argument could be made for including this in lang..
> [lang] Add equals(type[]) to NumberUtils
> ----------------------------------------
>
> Key: LANG-238
> URL: http://issues.apache.org/jira/browse/LANG-238
> Project: Commons Lang
> Issue Type: Improvement
> Affects Versions: Nightly Builds
> Environment: Operating System: other
> Platform: Other
> Reporter: Paul Benedict
> Priority: Minor
> Fix For: 3.0
>
>
> It would be useful to add an equals() method like the current min and max
> methods which take an array type and determine if all the values are equal.
> I have found myself in need of this often. I have to retrieve objects from
> multiple data sources in parallel to build an array of complex object. To
> ensure
> validity, I always compare that my sub-retrievals returned the same number of
> objects as expected.
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