sort problem sorting a generic list

[Paul]

Hi, I have a generic list and am able to sort it using the code below that I
have built in a class UserDefinedGroupSummary. There is an integer in the
class called GroupNumber and the sort by group number does return a list with
the group numbers sorted. The problem is when there is only one group number
in the list, it looks like it is still changing the order of the elements in
the list.
Any ideas, thanks.

I use grouplist.Sort();// to sort the group generic list

In the class I have
public static Comparison<UserDefinedGroupSummary> CompareGroup =
delegate(UserDefinedGroupSummary g1, UserDefinedGroupSummary g2)
{
return g1.GroupNumber.CompareTo(g2.GroupNumber);
};
#region IComparable<UserDefinedGroupSummary> Members

public int CompareTo(UserDefinedGroupSummary other)
{
return GroupNumber.CompareTo(other.GroupNumber);
}
#endregion

 

[sloan]

If you have a "tie" (result of 0) you need to break it, if you dont' want
random results.


public int CompareTo(UserDefinedGroupSummary other)
{
int returnValue = 0;

returnValue =GroupNumber.CompareTo(other.GroupNumber);

if (returnValue ==0)
{ returnValue = this.CreateDate.CompareTo(other.CreateDate); //
or some property
}

return returnValue;
}

pseudo code for you to experiment with.

 

[sloan]

Here is a sample of my LastName/FirstName sorter for a User object.


returnValue = this.LastName.CompareTo(other.LastName);

if (returnValue == 0) //tie

{

returnValue = this.FirstName.CompareTo(other.FirstName);

}

return returnValue ;


Same concept.......

 

[Paul]

Hi thanks for the response. I made the modification as suggested. I do not
have a row number but thinking I may need to add one and then if tie
condition have it sort on the row number. What I have below .Count is always
0 for all records so it still is mixing things up.
Thanks again

public int CompareTo(UserDefinedGroupSummary other)
{
int returnValue = 0;//added
returnValue=GroupNumber.CompareTo(other.GroupNumber);
if (returnValue == 0)
{
returnValue = this.Count.CompareTo(other.Count);//tie
}
return returnValue;
//orig return GroupNumber.CompareTo(other.GroupNumber);

}
--
Paul G
Software engineer.

Here is a sample of my LastName/FirstName sorter for a User object.


returnValue = this.LastName.CompareTo(other.LastName);

if (returnValue == 0) //tie

{

returnValue = this.FirstName.CompareTo(other.FirstName);

}

return returnValue ;


Same concept.......

 

[sloan]

You understand the concept, so now you have to find your solution.

If a two way tie isn't enough, then go to something else.

In my example...
LastName
FirstName

If I find out I have a bunch of "John Smith"'s in my collection, then I
could go to the SSN or something.

............

If you're using an IDataReader or something like that to populate, then yes,
you can can add an artificial "RowNumber" property if you want.
Its your call. The bottom line is that if you have a tie, you can't predict
the results unless you break the tie.


Good luck.

Hi thanks for the response. I made the modification as suggested. I do
not
have a row number but thinking I may need to add one and then if tie
condition have it sort on the row number. What I have below .Count is
always
0 for all records so it still is mixing things up.
Thanks again

public int CompareTo(UserDefinedGroupSummary other)
{
int returnValue = 0;//added
returnValue=GroupNumber.CompareTo(other.GroupNumber);
if (returnValue == 0)
{
returnValue = this.Count.CompareTo(other.Count);//tie
}
return returnValue;
//orig return GroupNumber.CompareTo(other.GroupNumber);

}

 

[sloan]

http://sholliday.spaces.live.com/Blog/cns!A68482B9628A842A!141.entry

That is a 1.1 article, however, there are a few 2.0 hints at the bottom.
having said that, I would keep away from the reflection based
comparer's/sorter's .... if I had any signficant sized lists.


..........

 

[Paul]

Ok thanks it works, just using an artificial row number. Guessing that
reflection based comparer's/sorter's can have an impact on performance.