Question

remove duplicates from list in C#

Asked by: R8VI

Hi,

I have create a list like so

List<Question> questions = new List<Question>();

which has following

questiontext, qid, and answer

What I want to do is remove any duplicates of question text so for example

row 1
questiontext = blue
qid = 2
answer = n

row 2
questiontext = Yellow
qid = 2
answer = n

row 3
questiontext = blue
qid = 2
answer =

so since questiontext is blue in row 1 and row 3 it sud remove all of row 3

Please help

Thanks,

R8VI

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Asked On
2009-10-30 at 06:52:26ID24858013
Tags

asp.net

,

c#

Topics

.NET

,

C# Programming Language

,

Programming for ASP.NET

Participating Experts
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Comments
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Answers

 

by: p_davisPosted on 2009-10-30 at 06:59:49ID: 25702987

List<Question> processed = new List<Question>();

foreach(Question q in questions)
{

     if(!processed.Contains(q))
             processed.Add(q);//at the end you will have no duplicates in processsed.
                                          //you might have to override the Equals method on you object.

}

other wise you might
List<Question> processed = new List<Question>();

foreach(Question q in questions)
{

     Question found = processed.Find(x=>x.questionText == q.questionText && x.qid == q.qid /*etc*/);//put in whatever criteria you wish
      if(found == null)
          processed.Add(q);

}

 

by: princeatapiPosted on 2009-10-30 at 07:11:20ID: 25703099

Try this
List<T> noDupes = withDupes.Distinct().ToList();

 

by: princeatapiPosted on 2009-10-30 at 07:13:50ID: 25703119

Try this for .NET 2.0

public IEnumerable<T> DedupCollection<T> ( IEnumerable<T> input ) {
    List<T> passedValues = new List<T>();
 
    //relatively simple dupe check alg used as example
    foreach( T item in input)
        if( passedValues.Contains(item) )
            continue;
        else {
            passedValues.Add(item)
            yield return item;
        }
}
                                              
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by: FernandoSotoPosted on 2009-10-30 at 07:33:04ID: 25703315

Hi R8VI;

This should give you what you need.

Fernando

            Hashtable ht = new Hashtable();
            for ( int i = questions.Count - 1; i >= 0; i-- )
            {
                try
                {
                    ht.Add(questions[i].questiontext, questions[i]);
                }
                catch 
                {
                    // Duplicates found 
                    questions.RemoveAt(i);
                }
            }

                                              
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by: FernandoSotoPosted on 2009-10-30 at 07:35:09ID: 25703339

Hi R8VI;

You will need to have this using statement for my solution.

using System.Collections;

Fernando

 

by: DaTribePosted on 2009-10-30 at 07:36:59ID: 25703364

I'll approach this from a different angle. Why not just disallow duplicates from being added to the list in the first place.

HashSet<Question> questions = new HasSet<Question>();

This routine will now eliminate any duplicates on adding the questions to the list.

DaTribe

public class Question : IEquatable<Question>
{
    ...
 
    bool Equals(Question other)
    {
       return String.Compare(questiontext, other.questiontext, true) == 0
    }
}

                                              
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