收集多维数组的列来设置

Question

我有一个属性 this.sudoku，它是一个 int[9][9] 数组。我需要将其中的一列放入集合中。

Set<Integer> sudoku_column = IntStream.range(0, 9)
                                      .map(i -> this.sudoku[i][column])
                                      .collect(Collectors.toSet());

我希望此集合中有一个列值。但它说 Collectors.toSet() 不能应用于链中的这个 collect 函数。有人可以解释为什么吗？

Answer 1

IntStream#map consumes an IntUnaryOperator which represents an operation on a single int-valued operand that produces an int-valued result thus the result is an IntStream, however IntStream does not have the collect overload you're attempt to use, which means you have a couple of options; i.e. either use IntStream#collect:

IntStream.range(0, 9)
         .collect(HashSet::new, (c, i) -> c.add(sudoku[i][column]), HashSet::addAll);

或使用 mapToObj 将 IntStream 转换为 Stream<Integer>，然后您可以调用 .collect(Collectors.toSet())。

IntStream.range(0, 9)
        .mapToObj(i -> this.sudoku[i][column])
        .collect(Collectors.toSet());

Answer 2

IntStream#map takes an IntUnaryOperator 是一个将 int 转换为另一个 int 的函数。

如果您想继续 IntStream. But if you need to collect the stream into a Set<Integer>, you need to turn your IntStream into a stream of boxed ints, a Stream<Integer>, by IntStream#boxed 也没关系。

.map(i -> this.sudoku[i][column])
.boxed()
.collect(Collectors.toSet());

Collectors.toSet() cannot be applied to this collect function in the chain

Collectors.toSet() return 一个 Collector 不符合 IntStream 中单个 collect(Supplier, ObjIntConsumer, BiConsumer) 方法的签名。不过，它适合 Stream.collect(Collector).

收集多维数组的列来设置

collecting column of multidimensional array to set

java

set

java-8

java-stream

collectors