Hello all,
Just say I have an arraylist of objects (all of the same type) and say these objects are 'Person' objects. So each person has instance variables. such as firstname, surname, etc.
I wish to sort this arraylist of person object references by surname. What is the easiest way to do this
Thank you
Chris
Make your Person class implement IComparable<Person>. Here's an example I've knocked up quickly:
class Person : IComparable<Person>
{
string name;
string surname;
public Person(string name, string surname)
{
this.name = name;
this.surname = surname;
}
public int CompareTo(Person other)
{
int compareResult = surname.CompareTo(other.surname);
if (compareResult != 0)
{
return compareResult;
}
return name.CompareTo(other.name);
}
}
public void TestSort()
{
List<Person> person = new List<Person>();
person.Add(new Person("Dave", "Jones"));
person.Add(new Person("Andy", "Jones"));
person.Add(new Person("Barry", "Anderson"));
person.Sort();
}
int CompareClientsByAge(Client c1, Client c2)
{
return c1.Age - c2.Age;
}
While I'm all in favor of a good shortcut, I'd still write that as:
int CompareClientsByAge(Client c1, Client c2)
{
return c1.Age.CompareTo(c2.Age);
}
for a few reasons:
Sorting 'complex' objects...
Spyder_Snyper
Thats really good!
Thanks Charles I'll test it out.
Cheers
Chris
chris bax
Hello,
Actually I am having a bit of trouble here.
m_data.Clients.Sort( CompareClientsByName ); -- In this line what is m_data
I'm a bit lost and have only been able to get the overide 'CompareTo' way to work (it sorste the array list by surname. I can't override it again (in order to sort be first name.
Any help is appreciated. I have included the code for my CompareTo method.
public int CompareTo(object o){
Person other = (Person) o;
int compareResult = surname.CompareTo(other.surname); if (compareResult != 0){
return compareResult;}
return name.CompareTo(other.name);}
Thank you
Chris
bslim
Hi,
You need something like this:
SomeFunc () {
m_data.Clients.Sort( CompareClientsByName );
m_data.Clients.Sort( CompareClientsByAge );
}
int CompareClientsByAge(Client c1, Client c2)
{
return c1.Age - c2.Age;
}
int CompareClientsByName(Client c1, Client c2)
{
return c1.Name.CompareTo( c2.Name );
}
Charles
trai_mv
It looks as if cverdon just copied a snippet of code from his application. "m_data.Clients" refers to a List<> object, so going back to our previous example, that code would be written as :
List<Person> person = new List<Person>();
person.Sort( CompareClientsByName );
In this case, the CompareTo doesn't enter into it at all. We are using the public void Sort (Comparison<T> comparison) overload of Sort, where Comparison<T> is a method which takes two Ts.
SO, to order by Last Name, First Name:
public int OrderSurnameGivenname(Person lhs, Person rhs)
{
int compareResult = lhs.surname.CompareTo(rhs.surname);
if (compareResult != 0)
{
return compareResult;
}
return name.CompareTo(other.name);
}
shailesh_ch
No it doesn't. (For this example, let's work with Int16s) Try: -30000 - +30000 = -60000, but as an Int16, that +5536, a positive result even though -30000 < +30000 (Int32s have the same problem but you have to work with number with a even larger magnatude)
. Yes, that's true....But it's not your program that we're worried about, but someone else's. So, when the other module crashes when it references your assembly, you can try to convince them that you followed the rules and they didn't, or you could just program defensively in the first place, and avoid the problem. This is one of the fundemental principles of library design: The library user should code assuming the looses interpretation of the docs ( <0, 0, >0), while the libray writer should code using the strictest interpreation (-1, 0, +1). That way, if either side slips up, the application still works.
Taliesin&#42;
Thanks very much for that.
So in our object class to implement the IComparable interface and then implement the compareTo method. So I'm guessing that when we call the sort it will call the CompareTo method we have manually implemented as opposed to the default one. Is this right
And finally, what if I have a complex object and wish to sort using a particular compareTo method at anyone time An example would be: Sometimes I awant to sort on surname, other times I wish to sort on 'address street name'.
Is this still the most efficient way
Thanks
Chris
twonjosh
Yes James guessed it right:
IDataContainer m_data = new DataContainer();
public class DataContainer : IDataContainer
{
private List<Client> m_clients = new List<Client>();
public List<Client> Clients
{
get { return m_clients; }
set { m_clients = value; }
}
}
http://msdn2.microsoft.com/en-gb/library/system.icomparable.compareto.aspx
I agree, but if it works in all cases and it respects the standards there is no problem in implementing integer comparison with a simple - operation
Regards,
Charles