Hi,

A Hashtable is the most efficient form of retrieval structure as long as

you have an efficient hash algorithm (seeded random number generator).

and the performance degradation with volume is negligible so long as the

system is using some form of extendable hashing.

Look up info on extensible hashing to see how it all works.

An example link is here:

http://feast.ucsd.edu/CSE232W99/Indexing/sld034.htm
although the 'good' hash algorithm he suggests is a poor one :)

The GetHashCode() in .Net uses a version of the Zobel/Ramakrishna algorithm

(the best performing algorithm I'm aware of) but has been adapted to

produce a guaranteed unique key (not necessary for a hash table but

sometimes required internally by .Net).

If you want to 'roll your own' for some obscure data structure then I've

attached an adaptation of the hash function below.

Cheers,

Jason

Public Function computeHashCode(ByVal StrToHash As String) As Integer

Dim c As Byte() =

System.Text.Encoding.UTF8().GetBytes(StrToHash.ToC harArray())

Dim h As Integer = 31 'seed chosen at random

Dim i As Integer

For i = 0 To c.Length - 1

' L=5, R=2 works well for ASCII input

h = (h Xor ((h * 32) + (h \ 4) + c(i))) And &HFFFF

Next

Return h

End Function

On Tue, 27 Jan 2004 09:48:26 +1300, Greg Bacchus wrote:

Hi,

I'm just concerned about storing a large amount of items in a Hashtable. It

seems to me that as the number of keys in the Hashtable increases, so does

the chance of key clashes.

Does anyone know about the performance with regards to this?

Cheers

Greg