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csharptoday_discuss thread: want to discuss sorting arrays of objects
Message #1 by "Chris Hart" <cahart@c...> on Mon, 10 Dec 2001 21:42:24 -0600
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If I have an array of objects, such as the array of Entry objects on page
816 of Chapter-24 in the "Beginning C#" book.
And I want to explicitly sort that array by calling the sort method of the
array class (ie., Array.Sort(entries) )
why do I get the following error at run-time:
"At least one object must implement IComparable."
An Entry obj has the following properties:
private String _filename;
private DateTime _timestamp;
private String _title;
private String _details;
I really don't care if I sort on _filename or _timestamp.
Would very much appreciate clarification on this.
Thanks in advance
Chris
Message #2 by "Frank Paris" <marshalt@s...> on 10 Dec 2001 21:23:17 -0800
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The Sort method must know how to compare two elements of your array. The
IComparable interface defines the CompareTo() method, which you must
implement in order to make the comparison. In your CompareTo() method
you would compare this._filename or this._timestamp to the _filename or
_timestamp in the Entry object input to your IComparable.CompareTo()
method and return a value telling the Sort method whether 'this' is
greater, equal to, or less than the input Entry.
Frank Paris
marshalt@s...
> -----Original Message-----
> From: Chris Hart [mailto:cahart@c...]
> Sent: Monday, December 10, 2001 7:42 PM
> To: C#Today Discuss
> Subject: [csharptoday_discuss] want to discuss sorting arrays
> of objects
>
>
> If I have an array of objects, such as the array of Entry
> objects on page 816 of Chapter-24 in the "Beginning C#" book.
> And I want to explicitly sort that array by calling the sort
> method of the array class (ie., Array.Sort(entries) ) why do
> I get the following error at run-time:
>
> "At least one object must implement IComparable."
>
> An Entry obj has the following properties:
> private String _filename;
> private DateTime _timestamp;
> private String _title;
> private String _details;
>
> I really don't care if I sort on _filename or _timestamp.
>
> Would very much appreciate clarification on this.
>
> Thanks in advance
> Chris
Message #3 by "Chris Hart" <cahart@c...> on Tue, 11 Dec 2001 08:24:16 -0600
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Hi Frank,
Thanks very much for taking the time to respond to my question.
After I submitted it I found an example in my "A Programmer's Intro. To C#"
book (pg. 298 for anyone interested) that showed exactly what you are
explaining.
I implemented a CompareTo method that compares the _timestamp property and I
now get the results I want.
Regards,
Chris
-----Original Message-----
From: Frank Paris [mailto:marshalt@s...]
Sent: Monday, December 10, 2001 11:23 PM
To: C#Today Discuss
Subject: [csharptoday_discuss] RE: want to discuss sorting arrays of
objects
The Sort method must know how to compare two elements of your array. The
IComparable interface defines the CompareTo() method, which you must
implement in order to make the comparison. In your CompareTo() method
you would compare this._filename or this._timestamp to the _filename or
_timestamp in the Entry object input to your IComparable.CompareTo()
method and return a value telling the Sort method whether 'this' is
greater, equal to, or less than the input Entry.
Frank Paris
marshalt@s...
> -----Original Message-----
> From: Chris Hart [mailto:cahart@c...]
> Sent: Monday, December 10, 2001 7:42 PM
> To: C#Today Discuss
> Subject: [csharptoday_discuss] want to discuss sorting arrays
> of objects
>
>
> If I have an array of objects, such as the array of Entry
> objects on page 816 of Chapter-24 in the "Beginning C#" book.
> And I want to explicitly sort that array by calling the sort
> method of the array class (ie., Array.Sort(entries) ) why do
> I get the following error at run-time:
>
> "At least one object must implement IComparable."
>
> An Entry obj has the following properties:
> private String _filename;
> private DateTime _timestamp;
> private String _title;
> private String _details;
>
> I really don't care if I sort on _filename or _timestamp.
>
> Would very much appreciate clarification on this.
>
> Thanks in advance
> Chris
cahart@c...
$subst('Email.Unsub')
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