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如何利用 Java 将学生成绩数据从行格式转换为列格式？
ID:17406 / 打印
java 数据转换：行转列
问题：
如何将以下源数据转化为期望的输出格式？
源数据：
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class studentid subject score class one 1 english 84 class one 1 math 77 class one 1 pe 69 class one 2 english 81 class one 2 math 80 ...
期望输出：
class studentid english math pe class one 1 84 77 69
解决方案：
可以通过行转列的操作实现此转换。 voici 使用 java 代码演示如何完成：
import java.util.hashmap; import java.util.list; import java.util.map; import java.util.stream.collectors; class rowtocolumntransformer { public static void main(string[] args) { // 源数据 list<studentdata> studentdatalist = list.of( new studentdata("class one", 1, "english", 84), new studentdata("class one", 1, "math", 77), new studentdata("class one", 1, "pe", 69), new studentdata("class one", 2, "english", 81), new studentdata("class one", 2, "math", 80) ); // 创建一个映射，使用 class 和 studentid 作为键，subject 和 score 作为值 map<string, map<string, integer>> subjectscoremap = new hashmap<>(); for (studentdata studentdata : studentdatalist) { string classandstudentid = studentdata.getclassandstudentid(); map<string, integer> scoremap = subjectscoremap.getordefault(classandstudentid, new hashmap<>()); scoremap.put(studentdata.getsubject(), studentdata.getscore()); subjectscoremap.put(classandstudentid, scoremap); } // 创建期望的输出 list<studentdata> transformeddatalist = subjectscoremap.entryset().stream() .map(entry -> new studentdata(entry.getkey(), entry.getvalue())) .collect(collectors.tolist()); // 打印输出 for (studentdata transformeddata : transformeddatalist) { system.out.println(transformeddata); } } private static class studentdata { private string classandstudentid; private map<string, integer> subjectscoremap; public studentdata(string classandstudentid, int studentid, string subject, int score) { this.classandstudentid = classandstudentid + "-" + studentid; this.subjectscoremap = map.of(subject, score); } public studentdata(string classandstudentid, map<string, integer> subjectscoremap) { this.classandstudentid = classandstudentid; this.subjectscoremap = subjectscoremap; } public string getclassandstudentid() { return classandstudentid; } public map<string, integer> getsubjectscoremap() { return subjectscoremap; } @override public string tostring() { return classandstudentid + " " + subjectscoremap.getordefault("english", 0) + " " + subjectscoremap.getordefault("math", 0) + " " + subjectscoremap.getordefault("pe", 0); } } }输出：
Class one-1 84 77 69 Class one-2 81 80 0
