NonEmptyVector

NonEmptyVector<A> is a sequence with at least one element. It holds a Vector and has the same costs.

Total operations

On a Vector, head, max or reduce can fail or return an Option, because the Vector may be empty. On a NonEmptyVector they return the value itself. The same holds for last, min, maxBy, minBy and the other reduce methods.

NonEmptyVector<Integer> scores = NonEmptyVector.of(7, 3, 9);
int best = scores.max(Integer::compare);
int total = scores.reduce(Integer::sum);
int first = scores.head();
// 9, 19, 7

The return-type contract

The return type tells you whether the result can be empty:

Returns	When	For example
NonEmptyVector	the operation keeps or grows the size	map, append, appendAll, sorted, distinct, zip
Vector	the operation may remove elements	filter, collect, tail, take, drop, remove
Option	you ask for a part that may not exist	find, tailNonEmpty(), initNonEmpty()

grouped returns a Vector of NonEmptyVectors, and groupBy a HashMap whose values are NonEmptyVectors. appendAll and prependAll accept a Vector that may be empty and still return a NonEmptyVector.

NonEmptyVector<Integer> grown = NonEmptyVector.of(1).appendAll(Vector.empty());
Vector<Integer> evens = NonEmptyVector.of(1, 2, 3).filter(n -> n % 2 == 0);
Option<NonEmptyVector<Integer>> rest = NonEmptyVector.of(1).tailNonEmpty();
// NonEmptyVector(1), Vector(2), None

flatMap takes a function that returns a NonEmptyVector, and keeps the result non-empty. flatMapAll takes a function that returns any Iterable, and returns a Vector.

Construction

Constructor	Returns
of(head, rest...), single(a)	NonEmptyVector<A>
fromIterable(head, Iterable tail)	NonEmptyVector<A>
fromVector(Vector), fromIterable(Iterable)	Option<NonEmptyVector<A>>
Vector.toNonEmptyVector()	Option<NonEmptyVector<A>>
unsafeFromVector(Vector)	NonEmptyVector<A>, or IllegalArgumentException when empty
static flatten(NonEmptyVector<NonEmptyVector<A>>)	NonEmptyVector<A>

Option<NonEmptyVector<String>> fromInput = Vector.of("a", "b").toNonEmptyVector();
Option<NonEmptyVector<String>> fromNothing = Vector.<String>empty().toNonEmptyVector();
// Some(NonEmptyVector(a, b)), None

Sharp edges

• A NonEmptyVector is not a Vector and is not equal to one with the same elements; compare through toVector().
• It is Iterable, but not a Traversable: a method that takes a Traversable needs toVector().
• Validation uses it for its errors, and Validation.forEach over a NonEmptyVector returns one (Validation).