removing duplicate objects in a list

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So I understand how to remove duplicates in a list when it comes to strings and int, etc by using Distinct() from Linq. But how do you remove duplicates based on a specific attribute of an object?

For example, I have a TimeMetric class. This TimeMetric class has two attributes: MetricText and MetricTime. I have a list of TimeMetrics called MetricList. I want to remove any duplicates TimeMetric with the same MetricText attribute.

Posted 13-Jul-12 12:38pm

shekarchee

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Sergey Alexandrovich Kryukov 13-Jul-12 18:44pm

Do you require to find an already implemented pattern, or do you agree to simply right it from scratch, without LINQ? You could just implement it ad-hoc or add your own extension method, both things are pretty easy...
--SA

Sergey Alexandrovich Kryukov 14-Jul-12 23:12pm

And please do not re-post. Ask one question on the topic and use "Improve question" if you need it.
--SA

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Clifford Nelson · Answer 1 · 2012-07-13T18:17:00

A little easier is to use the groupby, although a little confusing:

C#

var groups = strings.GroupBy(i => i.str1);
foreach (var group in groups)
{
    var firstGroup = group.First();
    Console.WriteLine(first.str1, first.str2}
}

I used the following class for this:

C#

public class test
{
    public string str1 { get; set; }
    public string str2 { get; set; }
}

**Zoltán Zörgő** · Answer 2 · 2012-07-14T21:24:00

Solution 3

See my answer to your other topic here: removing duplicate objects in a list based on its properties[^]

Posted 14-Jul-12 21:24pm

Zoltán Zörgő

Matt T Heffron · Answer 3 · 2012-07-13T13:35:00

Edited: I didn't follow the link in the solution posted by Zoltán Zörgő before my posting. It is essentially the same as what I posted here. I have upvoted his solution.

Distinct() has an overload that takes an IEqualityComparer<TSource> parameter. So you could implement that interface and then use the Distinct() pattern you already know.
Like this:

C#

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

namespace ConsoleApplication1
{
  class Program
  {
    static void Main(string[] args)
    {
      var metrics = new List<TimeMetric>();
      Random r = new Random();
      for (int i = 0; i < 10; i++)
      {
        var item = new TimeMetric();
        item.MetricText = (i | 1).ToString(); // ensure there are duplicate Text
        item.MetricTime = TimeSpan.FromTicks(r.Next()); // but not duplicate Time
        metrics.Add(item);
        Console.WriteLine("metric[{0}]: MetricText = \"{1}\", MetricTime = {2}",
                          i, item.MetricText, item.MetricTime);
      }
      var NoDuplicates = metrics.Distinct(new TimeMetricTextComparer());
      int ix = 0;
      foreach (var item in NoDuplicates)
      {
        Console.WriteLine("NoDuplicates[{0}]: MetricText = \"{1}\", MetricTime = {2}",
                          ix++, item.MetricText, item.MetricTime);
      }
    }
  }

  class TimeMetric
  {
    public string MetricText { get; set; }
    public TimeSpan MetricTime { get; set; }
  }

  class TimeMetricTextComparer : IEqualityComparer<TimeMetric>
  {
    #region IEqualityComparer<TimeMetric> Members
    public bool Equals(TimeMetric x, TimeMetric y)
    {
      return string.Equals(x.MetricText, y.MetricText);
    }
    public int GetHashCode(TimeMetric obj)
    {
      return obj.MetricText.GetHashCode();
    }
    #endregion
  }
}

In the comparer class, Equals and GetHashCode must be consistent. If Equals is true for two TimeMetric instances, then GetHashCode must return the same value for both.

removing duplicate objects in a list

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