LINQを使用して同じ値の列を列にグループ化します

Question

このような結果を得たLINQクエリがあります。被験者の数が固定されていない：

Student Subject Mark 
Adam  English 80 
Adam  Math  70 
Adam  Science 60 
Moses English 95 
Moses Science 75 

は、今私が望むすべては

Student English Math Science 
Adam 80  70  60 
Moses 95    75 

注を以下のようにそれを変換することです。被験者は知られており、固定されている場合は

Answer 1

てみコードをこの

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 
using System.Data; 

namespace ConsoleApplication12 
{ 
    class Program 
    { 
     static void Main(string[] args) 
     { 
      DataTable sourceTable = new DataTable(); 
      sourceTable.Columns.Add("Student", typeof(string)); 
      sourceTable.Columns.Add("Subject", typeof(string)); 
      sourceTable.Columns.Add("Mark", typeof(int)); 

      sourceTable.Rows.Add(new object[] { "Adam","English", 80}); 
      sourceTable.Rows.Add(new object[] { "Adam","Math", 70}); 
      sourceTable.Rows.Add(new object[] { "Adam","Science", 60}); 
      sourceTable.Rows.Add(new object[] { "Moses","English", 95}); 
      sourceTable.Rows.Add(new object[] { "Moses","Science", 75}); 

      List<string> subjects = sourceTable.AsEnumerable().Select(x => x.Field<string>("Subject")).Distinct().ToList(); 
      DataTable pivotTable = new DataTable(); 
      pivotTable.Columns.Add("Student", typeof(string)); 
      foreach(string subject in subjects) 
      { 
       pivotTable.Columns.Add(subject, typeof(int)); 
      } 
      var students = sourceTable.AsEnumerable() 
       .GroupBy(x => x.Field<string>("Student")).ToList(); 

      foreach (var student in students) 
      { 
       DataRow newRow = pivotTable.Rows.Add(); 
       newRow["Student"] = student.Key; 
       foreach (DataRow row in student) 
       { 
        newRow[row.Field<string>("Subject")] = row.Field<int>("Mark"); 
       } 

      } 
     } 
    } 
} 

Answer 2

あなたが使用できます。

var query = db.StudentMarks 
    .GroupBy(x => x.Student) 
    .Select(g => new { 
     Student = g.Key, 
     English = g.Where(x => x.Subject == "English").Sum(x=> x.Mark), 
     Math = g.Where(x => x.Subject == "Math").Sum(x=> x.Mark), 
     Science = g.Where(x => x.Subject == "Science").Sum(x=> x.Mark), 
    }); 

Answer 3

ようがあるでしょうあなたはどのように多くの科目がわからない場合情報をネストされた辞書に照合することができます。

var subjectMarksByStudent = new Dictionary<string, Dictionary<string, int>>(); 
foreach (var studentMark in studentMarks) 
{ 
    Dictionary<string, int> subjectsAndMarksForStudent; 
    if (subjectMarksByStudent.TryGetValue(studentMark.Name, out subjectsAndMarksForStudent)) 
    { 
     subjectsAndMarksForStudent.Add(studentMark.Subject, studentMark.Mark); 
    } 
    else 
    { 
     subjectMarksByStudent.Add(studentMark.Name, new Dictionary<string, int> {{ studentMark.Subject, studentMark.Mark }}); 
    } 
}