如何在 C# 中使用 Linq 查找最新员工工资？

Question

I got this challenging question online while solving c# problems, to find this using SQL is easy but using LINQ seems difficult for me. This is the data in the input.txt file.

22, Rajan Anand, Engineering, 1600000
23, Swati Patil, Testing, 800000
27, Vijay Chawda, Engineering, 800000
29, Basant Mahapatra, Engineering, 600000
32, Ajay Patel, Testing, 350000
34, Swaraj Birla, Testing, 350000

Output is: Engineering:600000 Testing: 350000

Please do change in processData function only. Help is appreciated.

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;

/* Don't change anything here.
 * Do not add any other imports. You need to write
 * this program using only these libraries 
 */

namespace ProgramNamespace
{
    public class Program
    {

        /* DO NOT CHANGE ANYTHING ABOVE THIS LINE */

        public static Dictionary<String, int> processData(
                                        IEnumerable<string> lines)
        {
            /* 
             * Do not make any changes outside this method.
             *
             * Modify this method to process `array` as indicated
             * in the question. At the end, return the size of the
             * array. 
             *
             * Do not print anything in this method
             *
             * Submit this entire program (not just this function)
             * as your answer
             */
            Dictionary<String, int> retVal = new Dictionary<String, int>();
            return retVal;
        }

        /* DO NOT CHANGE ANYTHING BELOW THIS LINE */

        static void Main(string[] args)
        {
            try
            {
                Dictionary<String, int> retVal = processData(
                                      File.ReadAllLines("input.txt"));
                File.WriteAllLines("output.txt",
                    retVal.Select(x => x.Key + ": " + x.Value).ToArray());
            }
            catch (IOException ex)
            {
                Console.WriteLine(ex.Message);
            }
        }

    }
}

Answer 1

return lines
  .Select(l=>l.Split(','))
  .GroupBy(i=>i[2])
  .ToDictionary(
    k=>k.Key, 
    v=>int.Parse(v.OrderByDescending(z=>int.Parse(z[0])).First()[3]));

Or more readable:

return lines
  .Select(l=>l.Split(','))
  .Select(z=>new {Id=int.Parse(z[0]), Name=z[1], Department=z[2], Salary=int.Parse(z[3])})
  .GroupBy(e=>e.Department)
  .ToDictionary(k=>k.Key,v=>v.OrderByDescending(z=>z.Id).First().Salary);

Answer 2

You can try below code in processData function, you will get your output:

Dictionary<String, int> retVal = new Dictionary<String, int>();

Dictionary<int, string> empWithDepart = lines.Select(x => x.Split(',')).ToDictionary(x => Convert.ToInt32(x[0]), x => Convert.ToString(x[2]));
Dictionary<int, int> empWithSalary = lines.Select(x => x.Split(',')).ToDictionary(x => Convert.ToInt32(x[0]), x => Convert.ToInt32(x[3]));
var departWithHighestEmpID = empWithDepart.OrderByDescending(x => x.Key).GroupBy(x => x.Value)
                               .ToDictionary(x => x.Key, x => x.FirstOrDefault().Key).ToList();
departWithHighestEmpID.Sort((pair1, pair2) => pair1.Key.CompareTo(pair2.Key));
foreach (var item in departWithHighestEmpID)
{
    retVal.Add(item.Key, empWithSalary[item.Value]);
}

return retVal;