生成笛卡尔乘积Java

Question

我正在尝试对一个后端服务器进行负载测试，并将一些配置解析到一个标签对象中。我正在尝试生成< code>Label对象的笛卡尔乘积，这将是一个< code>Metric对象。

Label {
   String name;
   String labe;
}

我有一个列表

[[name: "office_instance"value: "office_instance_0", name: "office_instance"value: "office_instance_1", name: "office_instance"value: "office_instance_2", name: "office_instance"value: "office_instance_3"], [name: "office_type"value: "office_type_0", name: "office_type"value: "office_type_1", name: "office_type"value: "office_type_2", name: "office_type"value: "office_type_3"], [name: "resource_type"value: "resource_type_0", name: "resource_type"value: "resource_type_1", name: "resource_type"value: "resource_type_2", name: "resource_type"value: "resource_type_3"], [name: "resource"value: "resource_0", name: "resource"value: "resource_1", name: "resource"value: "resource_2", name: "resource"value: "resource_3"], [name: "resource_group_name"value: "resource_group_name_0", name: "resource_group_name"value: "resource_group_name_1", name: "resource_group_name"value: "resource_group_name_2", name: "resource_group_name"value: "resource_group_name_3"], [name: "scope"value: "scope_0", name: "scope"value: "scope_1", name: "scope"value: "scope_2", name: "scope"value: "scope_3"]]

因为这是从配置生成的，所以生成时间序列的代码需要是动态的。在本例中，labelList的大小为5，每个单独的列表为4个标签。因此，度量对象的总数将为4*4*4*4*4。

度量对象的示例将是

[[ name: "office_instance"value: "office_instance_0", name: "office_type"value: "office_type_0", name: "resource_type"value: "resource_type_0", name: "resource"value: "resource_0", name: "resource_group_name"value: "resource_group_name_0", name: "scope"value: "scope_0"][name: "office_instance"value: "office_instance_0", name: "office_type"value: "office_type_0", name: "resource_type"value: "resource_type_0", name: "resource"value: "resource_0", name: "resource_group_name"value: "resource_group_name_0", name: "scope"value: "scope_1"]......]

生成指标有两种方法，一种是通过 addLabels 方法一次添加一个标签

 Metric.newBuilder().addLabels(Label obj).build()

或者通过< code>addAllLabels方法添加

 Metric.newBuilder().addAllLabels(List<Label> obj).build()

我试图以迭代/递归的方式做到这一点，但它变得非常复杂和混乱。我检查了是否有java8替代方案。如果我能够获得列表

我在这里引用了Java 8中流的笛卡尔乘积作为流（仅使用流）。但还是想不通。任何帮助将不胜感激。

编辑：发现番石榴有笛卡尔产品API，这可能会有所帮助，不确定它是否是最优化的。




Answer 1

在我看来，你需要一个递归函数。这就是我想出的：

public class Cartesian {

    public static void main(String[] args) {
        List<List<Label>> labelList = Arrays.asList(//
                Arrays.asList( //
                        new Label("office_instance", "office_instance_0"), //
                        new Label("office_instance", "office_instance_1") //
                ), //
                Arrays.asList( //
                        new Label("office_type", "office_type_0"), //
                        new Label("office_type", "office_type_1") //
                ), //
                Arrays.asList( //
                        new Label("resource_type", "resource_type_0"), //
                        new Label("resource_type", "resource_type_1") //
                )//

        );
        List<List<Label>> result = generateCombinations(labelList);

        System.out.println(result);
    }

    private static List<List<Label>> generateCombinations(List<List<Label>> labels) {
        List<List<Label>> result = new ArrayList<>();
        // for each label in first list
        // generate combinations of labels from the rest of the list
        for (Label label : labels.get(0)) {
            if (labels.size() > 1) {
                for (List<Label> entry : generateCombinations(labels.subList(1, labels.size()))) {
                    entry.add(label);
                    result.add(entry);
                }
            } else {
                // base case
                result.add(new ArrayList<>(Arrays.asList(label)));
            }
        }
        return result;
    }

    private static class Label {
        String name;
        String label;

        Label(String name, String label) {
            this.name = name;
            this.label = label;
        }

        @Override
        public String toString() {
            return "(name: " + name + ", label: " + label + ")";
        }
    }
}

为了简洁起见，我没有使用完整的列表。

输出（手动格式化）：

[
    [
        (name: resource_type, label: resource_type_0),
        (name: office_type, label: office_type_0),
        (name: office_instance, label: office_instance_0)
    ],
    [
        (name: resource_type, label: resource_type_1),
        (name: office_type, label: office_type_0),
        (name: office_instance, label: office_instance_0)
    ],
    [
        (name: resource_type, label: resource_type_0),
        (name: office_type, label: office_type_1),
        (name: office_instance, label: office_instance_0)
    ],
    [
        (name: resource_type, label: resource_type_1),
        (name: office_type, label: office_type_1),
        (name: office_instance, label: office_instance_0)
    ],
    [
        (name: resource_type, label: resource_type_0),
        (name: office_type, label: office_type_0),
        (name: office_instance, label: office_instance_1)
    ],
    [
        (name: resource_type, label: resource_type_1),
        (name: office_type, label: office_type_0),
        (name: office_instance, label: office_instance_1)
    ],
    [
        (name: resource_type, label: resource_type_0),
        (name: office_type, label: office_type_1),
        (name: office_instance, label: office_instance_1)
    ],
    [
        (name: resource_type, label: resource_type_1),
        (name: office_type, label: office_type_1),
        (name: office_instance, label: office_instance_1)
    ]
]