digitalmars.D.learn - Associative arrays question

Robby (8/8) Dec 31 2007 It's probably quite simple, but for some reason I seem to be in a blank.

Derek Parnell (20/32) Dec 31 2007 I would have thought that

Robby (31/71) Dec 31 2007 Thanks!. Dunno what I was seeing, took the documentation one way too

Jarrett Billingsley (12/16) Dec 31 2007 The AA implementation in D uses a form of separate chaining where each s...

Jarrett Billingsley (5/14) Dec 31 2007 I forgot where I was headed with this :) the thing is that it doesn't

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Robby (3/35) Dec 31 2007 ta!

Robby <robby.lansaw gmail.com> writes:

It's probably quite simple, but for some reason I seem to be in a blank.

I'm trying to write an associative array where a enum is the key and a 
array of classes is the value.

So given a simple example
enum T {Zero,One,Two,Three,Four,Five}
class L {}

How would I write the declaration for an associative array?

I thought it may be  L[T[]][] but it's clearly not, help?

Dec 31 2007

Derek Parnell <derek psych.ward> writes:

On Mon, 31 Dec 2007 04:20:34 -0500, Robby wrote:

 It's probably quite simple, but for some reason I seem to be in a blank.
 
 I'm trying to write an associative array where a enum is the key and a 
 array of classes is the value.
 
 So given a simple example
 enum T {Zero,One,Two,Three,Four,Five}
 class L {}
 
 How would I write the declaration for an associative array?
 
 I thought it may be  L[T[]][] but it's clearly not, help?

I would have thought that 
   
   L[][T] myAA;

   myAA[One] = new L;

would be it.

An array of classes ... L[]

The key is an enum (T) ... [T]

But did you mean that each element in the AA is an array of classes? In
that case ...

   L[][][T] myAA;

   L[] classarray;

   classarray ~= new L;
   classarray ~= new L;
   classarray ~= new L;

   myAA[One] = classarray;

-- 
Derek Parnell
Melbourne, Australia
skype: derek.j.parnell

Dec 31 2007

Robby <robby.lansaw gmail.com> writes:

Derek Parnell wrote:
 On Mon, 31 Dec 2007 04:20:34 -0500, Robby wrote:
 
 It's probably quite simple, but for some reason I seem to be in a blank.

 I'm trying to write an associative array where a enum is the key and a 
 array of classes is the value.

 So given a simple example
 enum T {Zero,One,Two,Three,Four,Five}
 class L {}

 How would I write the declaration for an associative array?

 I thought it may be  L[T[]][] but it's clearly not, help?

 
 I would have thought that 
    
    L[][T] myAA;
 
    myAA[One] = new L;
 
 would be it.
 
 An array of classes ... L[]
 
 The key is an enum (T) ... [T]
 
 But did you mean that each element in the AA is an array of classes? In
 that case ...
 
    L[][][T] myAA;
 
    L[] classarray;
 
    classarray ~= new L;
    classarray ~= new L;
    classarray ~= new L;
 
    myAA[One] = classarray;
 

Thanks!. Dunno what I was seeing, took the documentation one way too 
literal, I think. First one worked a treat.

I'm assuming that .rehash isn't really going to do much considering I'm 
using ints as the keys? Any real performance pitfalls when it comes to 
associative arrays that's not been documented to watch for?

~Robby

class L {}
enum T {Zero,One,Two,Three,Four,Five}
//....
	
		L y = new L();
		L x = new L();
		L z = new L();
		L[][T] tested;
	{
		tested[T.One] = [y, x, z];
		tested[T.One] ~= y;
		tested[T.One] ~= x;
		tested[T.One] ~= z;
		tested[T.Two] ~= [x, y];
		tested[T.Five] ~= x;
	}
	L[] curious = tested[T.One];
	
	{
		assert ((T.Four in tested) is null);
		assert (curious.length == 6);
		assert (tested[T.Five].length == 1);
		assert (tested.keys.length == 3);
	}

Dec 31 2007

"Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:

"Robby" <robby.lansaw gmail.com> wrote in message 
news:flahhv$ibd$1 digitalmars.com...

 I'm assuming that .rehash isn't really going to do much considering I'm 
 using ints as the keys?

The AA implementation in D uses a form of separate chaining where each slot 
in the hashtable points to a data structure used to resolve collisions.  In 
the case of the D AAs, it uses a binary tree at each slot.

What rehash does is makes the hash table bigger and reinserts all the keys 
into it.  If it's bigger in one direction, it'll be smaller in the other --  
that is, the average depth of each tree will get smaller, maybe even as 
small as 1 node for each tree, making lookups faster.

 Any real performance pitfalls when it comes

to
 associative arrays that's not been documented to watch for?

As long as you don't need to _duplicate_ them they should be quite 
performant.

Dec 31 2007

"Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:

"Jarrett Billingsley" <kb3ctd2 yahoo.com> wrote in message 
news:flavc0$1f0e$1 digitalmars.com...

 I'm assuming that .rehash isn't really going to do much considering I'm 
 using ints as the keys?

 The AA implementation in D uses a form of separate chaining where each 
 slot in the hashtable points to a data structure used to resolve 
 collisions.  In the case of the D AAs, it uses a binary tree at each slot.

 What rehash does is makes the hash table bigger and reinserts all the keys 
 into it.  If it's bigger in one direction, it'll be smaller in the 
 other --  that is, the average depth of each tree will get smaller, maybe 
 even as small as 1 node for each tree, making lookups faster.

I forgot where I was headed with this :)  the thing is that it doesn't 
really matter what type your keys are, .rehash should yield about the same 
speedup.

Dec 31 2007

=?ISO-8859-1?Q?=22J=E9r=F4me_M=2E_Berger=22?= <jeberger free.fr> writes:

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Robby wrote:
 It's probably quite simple, but for some reason I seem to be in a blank.
 
 I'm trying to write an associative array where a enum is the key and a
 array of classes is the value.
 
 So given a simple example
 enum T {Zero,One,Two,Three,Four,Five}
 class L {}
 
 How would I write the declaration for an associative array?
 
 I thought it may be  L[T[]][] but it's clearly not, help?

	Wouldn't it be L[][T]?

		Jerome
- --
+------------------------- Jerome M. BERGER ---------------------+
|    mailto:jeberger free.fr      | ICQ:    238062172            |
|    http://jeberger.free.fr/     | Jabber: jeberger jabber.fr   |
+---------------------------------+------------------------------+
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Dec 31 2007

Robby <robby.lansaw gmail.com> writes:

ta!
~Robby
J�r�me M. Berger wrote:
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 Hash: SHA1
 
 Robby wrote:
 It's probably quite simple, but for some reason I seem to be in a blank.

 I'm trying to write an associative array where a enum is the key and a
 array of classes is the value.

 So given a simple example
 enum T {Zero,One,Two,Three,Four,Five}
 class L {}

 How would I write the declaration for an associative array?

 I thought it may be  L[T[]][] but it's clearly not, help?

 
 	Wouldn't it be L[][T]?
 
 		Jerome
 - --
 +------------------------- Jerome M. BERGER ---------------------+
 |    mailto:jeberger free.fr      | ICQ:    238062172            |
 |    http://jeberger.free.fr/     | Jabber: jeberger jabber.fr   |
 +---------------------------------+------------------------------+
 -----BEGIN PGP SIGNATURE-----
 Version: GnuPG v1.4.7 (GNU/Linux)
 
 iD8DBQFHeLzUd0kWM4JG3k8RAtXFAJ9g6lHfhjg9YHZx3BEedlvs2oOc+QCghKVY
 JKj2AwDY+DTaGMJQ8PS8qNU=
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Dec 31 2007

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