Generic method to remove items from list

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Hi all, i have query and i would be really thankful if you could help me.
I have list<customer> with a property name SNO.

I have written a code

Public Void delete(List<Customer> dataList,String MatchedSno)
{
if(!String.IsNullOrEmpty(MatchedSno))
dataList.RemoveAll(a=>a.SNO==Convert.ToInt32(MatchedSno));
else
dataList.RemoveRange(1,dataList.Count-1);

}

But i want to create a generic method with List of Type <t> and now want to achieve the Same i.e.

Public Void delete<T>(List<T> dataList,String MatchedSno)
{
if(!String.IsNullOrEmpty(MatchedSno))
dataList.RemoveAll(a=>a.SNO==Convert.ToInt32(MatchedSno));
else
dataList.RemoveRange(1,dataList.Count-1);

}

Please give me an optimized solution for this.
Thank You

Posted 13-Nov-14 8:52am

Member 10582972

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Comments

Tomas Takac 13-Nov-14 15:10pm

Do you expect all the objects will have a SNO property? Or the key will be different for each class?

PIEBALDconsult 13-Nov-14 15:17pm

Unrelated:
Convert.ToInt32(MatchedSno));
If you don't want a string, don't pass in a string. Perform the conversion/parsing before calling the method.

Other than that, you may need a where clause to say that type T must be a type with a SNO.

Member 10582972 13-Nov-14 15:27pm

I have only 1 class Customer and SNO is its property,so all object will have SNO property

Tomas Takac 13-Nov-14 15:37pm

Then what do you need a generic method for?

BillWoodruff 14-Nov-14 1:51am

That's a very good question, Tomas, but, let's see the OP wanting to know how to do it generically is a sign they want to learn (yes, I try to be an optimist) :)

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Sergey Alexandrovich Kryukov · Answer 1 · 2014-11-13T09:33:00

Generics only makes sense if you really have different type for the list element, and all those types have a common (inherited) member to be used to to filter out the objects to be removed (or provide any common functionality at all). Then you would use generic type constraints to identify this common type. As you did not specify it, the question does not make sense. However, the idea to use generics may make sense, if you do what I mentioned above.

Besides, using string parameter in your delete method is not just silly, it's a crime (against yourself). You always compare integer property/field, so it should be integer parameter. And, if you parse a string to integer (or anything), uses int.Parse, not Convert. Finally, your code samples could not compile, because C# is case-sensitive. Why posting not real code?

Let me illustrate the idea on a simple example, which may not match your case:

C#

interface ISno
{
    int Sno { get; set; }
}
class Customer : ISno
{
    public int Sno { get; set; }
}

static class Test
{
    internal static void SelectiveDeleteSno<T>(List<T> list, int snoToMatch)
        where T : ISno // this constraint give access to ISno.Sno
    {
        list.RemoveAll(a => a.Sno == snoToMatch); // now you can do it
    }
}

So, if you have anything to specify the constraint, you can do it. If you did not have filtering and had to do something with some collection without using any knowledge on the elements, it could be any non-specified element type, so generic constraint would not be needed.

—SA

Matt T Heffron · Answer 2 · 2014-11-13T09:41:00

The way I can see to accomplish what you seem to want is:
Pass a delegate to the method that pulls out the value:

C#

public void delete<T>(List<T> dataList, Func<T, int> getSno, string MatchedSno)
{
  if(!string.IsNullOrEmpty(MatchedSno))
  {
    int match = Convert.ToInt32(MatchedSno);
    dataList.RemoveAll(a => getSno(a) == match);
  }
  else
    dataList.RemoveRange(1, dataList.Count-1);
}

Note that I convert MatchedSno to an integer only once, not every time in the lambda. Using int.TryParse() would be better than Convert.ToInt32(), you can handle errors more cleanly.

BillWoodruff · Answer 3 · 2014-11-13T09:47:00

The interesting challenge here is how to make this a generic method, but ensure that every List passed into it for manipulation implements a Property named 'Sno.

The way that is done is with a method constraint based on an Interface:

C#

public interface ISno
{
    int Sno { set; get; }
}

public void delete<t>(List<t> dataList, string MatchedSno) where T : ISno
{
    if (string.IsNullOrEmpty(MatchedSno))
    {
        dataList.RemoveRange(1,dataList.Count-1);
        return;
    }

    int intSNO = Convert.ToInt32(MatchedSno);

    dataList.RemoveAll(itm => itm.Sno == intSNO);            
}</t></t>

Test: Define two classes, one that implements ISno and one that doesn't:

C#

        public class HasSno : ISno
{
    public int Sno { set; get; }

    public HasSno(int sno)
    {
        Sno = sno;
    }
}

public class NoSno
{
    public int Sno { set; get; }

    public NoSno(int sno)
    {
        Sno = sno;
    }
}

Now we can test:

C#

private void SomeButton_Click(object sender, EventArgs e)
{
    var listHasSno = new List<hassno>();
    var listNoSno = new List<nosno>();

    for (int i = 0; i < 30; i++)
    {
        int m = i % 5; // value in series 0~4

        listHasSno.Add(new HasSno(m));

        listNoSno.Add(new NoSno(m));
    }

    delete(listHasSno, "3");

    // confirm all 'HasSno in list with 'Sno == 3 are deleted
    foreach (var sno in listHasSno) Console.WriteLine(sno.Sno);

    // this will fail:
    // delete(listNoSno, "2");
    // ftype 'noSno cannot be used as type parameter 'T' 
    // in the generic type or method delete<t>(System.Collections.Generic.List<t>, string)'.
    // There is no implicit reference conversion from 'noSno' to 'ISno'
}</t></t></nosno></hassno>

Generic method to remove items from list

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