Re: Finding distinct elements!

[Jon Skeet [C# MVP]]

On Jun 13, 2:38 pm, CSharper <[e-mail]:

here is the code

<snip>

Your Person class doesn't override Equals or GetHashCode. Therefore
every Person is distinct.

Jon

[CSharper]

On Jun 13, 9:18 am, "Jon Skeet [C# MVP]" <[e-mail]:

On Jun 13, 2:38 pm, CSharper <[e-mail]:

here is the code

<snip>

Your Person class doesn't override Equals or GetHashCode. Therefore
every Person is distinct.

Jon

Hi Jon,

Thanks and I have added following method and put a break point in the
method and I noticed the method never get called.

public override bool Equals(object obj)
{
if (obj == null) return false;
if (this.GetType() != obj.GetType()) return false;
Person p = (Person)obj;
return this.Name.Equals(p.Name);
}

Thanks,

[Jon Skeet [C# MVP]]

On Jun 13, 5:10 pm, CSharper <[e-mail]:

Thanks and I have added following method and put a break point in the
method and I noticed the method never get called.

<snip>

Did you override GetHashCode as well? If not, each Person would
(probably) have a distinct hash code, and thus the Distinct() method
would quite reasonably assume they weren't equal, without ever calling
your Equals method.

Jon

[CSharper]

On Jun 13, 11:23 am, "Jon Skeet [C# MVP]" <[e-mail]:

On Jun 13, 5:10 pm, CSharper <[e-mail]:

Thanks and I have added following method and put a break point in the
method and I noticed the method never get called.

<snip>

Did you override GetHashCode as well? If not, each Person would
(probably) have a distinct hash code, and thus the Distinct() method
would quite reasonably assume they weren't equal, without ever calling
your Equals method.

Jon

Hi Jon,

Thanks again. Do you think the following is the correct implementation
of GetHashCode?

public override int GetHashCode()
{
return this.Name.GetHashCode();
}

[Jon Skeet [C# MVP]]

On Jun 13, 5:42 pm, CSharper <[e-mail]:

Thanks again. Do you think the following is the correct implementation
of GetHashCode?

public override int GetHashCode()
{
return this.Name.GetHashCode();
}

That's fine as long as Name isn't null.

Are you sure that you really want to only judge equality by name
though? Why not include age and gender? (Date of birth is generally
better than age, btw - it doesn't change over time.) If this is just
for the purposes of learning about Distinct() that's fine, but
otherwise you might want to implement IEqualityComparer<Person>
instead (e.g. as a NameComparer). I haven't checked whether or not
Distinct can optionally take an IEqualityComparer, but I'd be
surprised if it couldn't.

Jon

[CSharper]

On Jun 13, 11:58 am, "Jon Skeet [C# MVP]" <[e-mail]:

On Jun 13, 5:42 pm, CSharper <[e-mail]:

Thanks again. Do you think the following is the correct implementation
of GetHashCode?

public override int GetHashCode()
{
return this.Name.GetHashCode();
}

That's fine as long as Name isn't null.

Are you sure that you really want to only judge equality by name
though? Why not include age and gender? (Date of birth is generally
better than age, btw - it doesn't change over time.) If this is just
for the purposes of learning about Distinct() that's fine, but
otherwise you might want to implement IEqualityComparer<Person>
instead (e.g. as a NameComparer). I haven't checked whether or not
Distinct can optionally take an IEqualityComparer, but I'd be
surprised if it couldn't.

Jon

Thank you very much, you gave me good direction for me to take
further.
As always thank you for the help.