Nathan Blomquist created COLLECTIONS-511:
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Summary: CollectionUtils.bisect(...), this would be a combination
of Select and SelectRejected
Key: COLLECTIONS-511
URL: https://issues.apache.org/jira/browse/COLLECTIONS-511
Project: Commons Collections
Issue Type: New Feature
Components: Collection
Reporter: Nathan Blomquist
Priority: Trivial
I recently needed a way to use a Predicate to select things from a list, but I
also wanted to know which ones failed the predicate test.
I wanted the following, but with one iteration instead of two:
{code}
List originalList = (...)
Predicate p = (...)
Collection selected = CollectionUtils.select(originalList, p);
Collection rejected = CollectionUtils.selectRejected(originalList, p);
// handle the selected cases (save them or whatnot)
// now throw an error message or handle the rejected cases
{code}
This is what I came up with based on the CollectionUtils.select(...) method:
{code:java}
public static <O, R extends Collection<? super O>> void bisect(
final Iterable<? extends O> inputCollection,
final Predicate<? super O> predicate,
final R selectedCollection,
final R rejectedCollection) {
if (inputCollection != null && predicate != null) {
for (final O item : inputCollection) {
if (predicate.evaluate(item)) {
selectedCollection.add(item);
}else{
rejectedCollection.add(item);
}
}
}
}
public static void main(String[] args){
// this will test the bisection code
List<String> original = Arrays.asList(
"testString1",
"testString2",
"testString3",
"String1",
"String2",
"String3",
"testString4",
"String4",
"testString5"
);
List<String> selected = new ArrayList<String>();
List<String> rejected = new ArrayList<String>();
Predicate<String> beginsWithTestPredicate =
new Predicate<String>() {
public boolean evaluate(String object) {
return object.startsWith("test");
}
};
bisect(original, beginsWithTestPredicate, selected, rejected);
System.out.println("Size of selected (should be 5):"
+ selected.size());
System.out.println("Size of rejected (should be 4):"
+ rejected.size());
}
{code}
This will of course throw a NullPointerException if either output collection is
null. This seems appropriate since we need to return two outputs anyway.
Not sure if *bisect* is the best name, but this method will split the original
into two pieces. https://www.google.com/#q=define+bisect
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