英文:
Dynamic Grouping using groupby() in java
问题
我正在处理一些场景。
在这种情况下，用户选择了一些列，然后对它们进行分组并显示出来。
我已经使用条件完成了，并且现在我想使用 Java 的 groupby() 函数来进行分组。
考虑我有一个实体类 Employee：
package com.demo;public class Employee {int id;String name;String address;String phoneno;String designation;public Employee(int id, String name, String address, String phoneno, String designation) {super();this.id = id;this.name = name;this.address = address;this.phoneno = phoneno;this.designation = designation;}}// getter and setters
我已经创建了另一个用于分组的类：
public class GroupHere {public static void main(String arg[]) {Function<Employee, List<Object>> classifier = (emp) ->Arrays.<Object>asList(emp.getAddress(), emp.getName());Map<Employee, Long> groupedEmployee = employee.stream().collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));System.out.println("key" + groupedEmployee.keySet());System.out.println("Grouped by" + groupedEmployee);}}
现在我想要动态创建我的分类器，所以当用户选择了“name”和“phoneno”时，分类器应该包含这些属性的 getter 方法。
我在这里感到困惑。
此外，当用户选择属性/列时，详细信息以 JSON 格式给出。
{[ attributes: name, groupable: true ],[ attributes: phoneno, groupable: true ]}
我如何将 attributes 映射到 Employee 的 getters 中，并添加到 classifier 中呢？
或者是否有其他方法可以对这些属性进行分组？
英文:
I am working on some scenario.
where the user selects some columns and the grouping on them is done and displayed.
I have done using criteria and now I want to use java groupby() to group.
Consider I have an entity Employee:
package com.demo;public class Employee {int id;String name;String address;String phoneno;String designation;public Employee(int id, String name, String address, String phoneno, String designation) {super();this.id = id;this.name = name;this.address = address;this.phoneno = phoneno;this.designation = designation;}}// getter and setters
I have created another class for grouping
public class GroupHere {public static void main(String arg[]) {Function<Employee, List<Object>> classifier = (emp) ->Arrays.<Object>asList(emp.getAddress(),emp.getName());Map<Employee, Long> groupedEmployee = employee.stream().collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));System.out.println("key" + groupedEmployee .keySet());System.out.println("Grouped by" + groupedEmployee );}}
Now I wanted to dynamically create my classifier so when the user selects '''name''' and '''phoneno'''
the classifier should have these getters in it.
I am confused here.
Also when user selects the attributes/column that details is in JSON.
{[ attributes: name, groupable: true ],[ attributes: phoneno, groupable: true ]}
How can I map the attributes with the getters of Employee and add into classifier ?
Or is their any other way to group this attributes?
答案1
得分: 4
你可以通过使用从属性名称到属性提取器的映射来实现，即：
Map<String, Function<Employee, Object>> extractors = new HashMap<>();extractors.put("name", Employee::getName);extractors.put("address", Employee::getAddress);extractors.put("phoneno", Employee::getPhoneno);extractors.put("designation", Employee::getDesignation);
一旦你有了这个映射，你可以使用它动态地创建分类器：
List<String> attributes = ...; // 从 JSON 中获取属性（留作练习）Function<Employee, List<Object>> classifier = emp -> attributes.stream().map(attr -> extractors.get(attr).apply(emp)).collect(Collectors.toList());
现在，你可以使用这个分类器来分组员工：
Map<List<Object>, Long> groupedEmployees = employees.stream().collect(Collectors.groupingBy(classifier, Collectors.counting()));
这样，你就可以使用这个分类器来分组员工了。
英文:
You could do it by using a map from attribute names to attribute extractors, i.e:
Map<String, Function<Employee, Object>> extractors = new HashMap<>();extractors.put("name", Employee::getName);extractors.put("address", Employee::getAddress);extractors.put("phoneno", Employee::getPhoneno);extractors.put("designation", Employee::getDesignation);
Once you have this map, you can use it to create your classifier dynamically:
List<String> attributes = ...; // get attributes from JSON (left as exercise)Function<Employee, List<Object>> classifier = emp -> attributes.stream().map(attr -> extractors.get(attr).apply(emp)).collect(Collectors.toList());
Now, you can use this classifier to gruop the employees:
Map<List<Object>, Long> groupedEmployees = employees.stream().collect(Collectors.groupingBy(classifier, Collectors.counting()));
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。
评论