How do I hash this ?

[Whybother]

I have 82,160 3 number combinations (non repeating, like one set of 1,2,3 ;
not like 1,2,2) that I'd like create hash keys for with out collision, if
possible. I tried SuperFastHash and when I tried loading them to my database
I got some primary key failures which would indicate matching keys.

I'd like to apply any solution to 4 & 5 number combinations as well.
I'm open any ideas or thoughts.

Thanks
Best Regards.

[Alf P. Steinbach]

* Whybother:

I have 82,160 3 number combinations (non repeating, like one set of 1,2,3 ;
not like 1,2,2) that I'd like create hash keys for with out collision, if
possible. I tried SuperFastHash and when I tried loading them to my database
I got some primary key failures which would indicate matching keys.

I'd like to apply any solution to 4 & 5 number combinations as well.
I'm open any ideas or thoughts.

What is the C++ question?

In other words, please post this q to e.g.[comp.programming].

It's off-topic here.

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

[Ian Collins]

Whybother wrote:

I have 82,160 3 number combinations (non repeating, like one set of 1,2,3 ;
not like 1,2,2) that I'd like create hash keys for with out collision, if
possible. I tried SuperFastHash and when I tried loading them to my database
I got some primary key failures which would indicate matching keys.

I'd like to apply any solution to 4 & 5 number combinations as well.
I'm open any ideas or thoughts.

How big are the number and how big is the required hash?

--
Ian Collins.

[Whybother]

"Ian Collins" <ia******@hotmail.com> wrote in message
news:11***************@drone2-svc-skyt.qsi.net.nz...

Whybother wrote:

I have 82,160 3 number combinations (non repeating, like one set of 1,2,3
; not like 1,2,2) that I'd like create hash keys for with out collision,
if possible. I tried SuperFastHash and when I tried loading them to my
database I got some primary key failures which would indicate matching
keys.

I'd like to apply any solution to 4 & 5 number combinations as well.
I'm open any ideas or thoughts.

How big are the number and how big is the required hash?

--
Ian Collins.

the numbers run from 1-80 and the requirement is that each has is unique

[Maxim Yegorushkin]

Whybother wrote:

"Ian Collins" <ia******@hotmail.com> wrote in message
news:11***************@drone2-svc-skyt.qsi.net.nz...

Whybother wrote:

I have 82,160 3 number combinations (non repeating, like one set of 1,2,3
; not like 1,2,2) that I'd like create hash keys for with out collision,
if possible. I tried SuperFastHash and when I tried loading them to my
database I got some primary key failures which would indicate matching
keys.

I'd like to apply any solution to 4 & 5 number combinations as well.
I'm open any ideas or thoughts.

How big are the number and how big is the required hash?

the numbers run from 1-80 and the requirement is that each has is unique

It's only 80^3 combinations = 512000. An array of 512000 elements would
do the trick.

[Whybother]

"Maxim Yegorushkin" <ma***************@gmail.com> wrote in message
news:11**********************@f14g2000cwb.googlegr oups.com...

Whybother wrote:

"Ian Collins" <ia******@hotmail.com> wrote in message
news:11***************@drone2-svc-skyt.qsi.net.nz...

> Whybother wrote:
>> I have 82,160 3 number combinations (non repeating, like one set of
>> 1,2,3
>> ; not like 1,2,2) that I'd like create hash keys for with out
>> collision,
>> if possible. I tried SuperFastHash and when I tried loading them to my
>> database I got some primary key failures which would indicate matching
>> keys.
>>
>> I'd like to apply any solution to 4 & 5 number combinations as well.
>> I'm open any ideas or thoughts.
>>
> How big are the number and how big is the required hash?

the numbers run from 1-80 and the requirement is that each has is unique

It's only 80^3 combinations = 512000. An array of 512000 elements would
do the trick.

Thats 80 to the third power, I'm talking about combinations, 80 choose 3 or
in excel combin(80,3). is 82,160. Thats not much and looking that up in a
database is quick too but when I get to 80 choose 5 , now we're talking
about 24 million and takes a little while to query the database thus the
plan to try to hash them so that its a matter of a quick look up of the hash
number.

thanks though.

[Maxim Yegorushkin]

Whybother wrote:

[]

It's only 80^3 combinations = 512000. An array of 512000 elements would
do the trick.

Thats 80 to the third power, I'm talking about combinations, 80 choose 3 or
in excel combin(80,3). is 82,160. Thats not much and looking that up in a
database is quick too but when I get to 80 choose 5 , now we're talking
about 24 million and takes a little while to query the database thus the
plan to try to hash them so that its a matter of a quick look up of the hash
number.

There is no way to create a hash with N buckets for [0, M) element
range, N < M, without collisions, unless you know all elements in
advance, and even then that may not be possible.

[Michiel.Salters]

Maxim Yegorushkin wrote:

Whybother wrote:

[]

It's only 80^3 combinations = 512000. An array of 512000 elements would
do the trick.

Thats 80 to the third power, I'm talking about combinations, 80 choose 3 or
in excel combin(80,3). is 82,160. Thats not much and looking that up in a
database is quick too but when I get to 80 choose 5 , now we're talking
about 24 million and takes a little while to query the database thus the
plan to try to hash them so that its a matter of a quick look up of the hash
number.

There is no way to create a hash with N buckets for [0, M) element
range, N < M, without collisions, unless you know all elements in
advance, and even then that may not be possible.

He knows all elements in advance, and furthermore, in his case he
probably
wants N==M.

If I read it correctly, he wants to hash a key {C1,C2,C3} where
0<=C1<C2<C3<80. That's not really a C++ question, though. At least,
there is no standard C++ library function for that.

I'd hash {C1,C2,C3} as (C1*choose(80-C1,2) + hash {C2,C3})

HTH,
Michiel Salters

[Whybother]

<Mi*************@tomtom.com> wrote in message
news:11*********************@z14g2000cwz.googlegro ups.com...

Maxim Yegorushkin wrote:

Whybother wrote:

[]

> > It's only 80^3 combinations = 512000. An array of 512000 elements
> > would
> > do the trick.
> >
>
> Thats 80 to the third power, I'm talking about combinations, 80 choose
> 3 or
> in excel combin(80,3). is 82,160. Thats not much and looking that up in
> a
> database is quick too but when I get to 80 choose 5 , now we're talking
> about 24 million and takes a little while to query the database thus
> the
> plan to try to hash them so that its a matter of a quick look up of the
> hash
> number.

There is no way to create a hash with N buckets for [0, M) element
range, N < M, without collisions, unless you know all elements in
advance, and even then that may not be possible.

He knows all elements in advance, and furthermore, in his case he
probably
wants N==M.

If I read it correctly, he wants to hash a key {C1,C2,C3} where
0<=C1<C2<C3<80. That's not really a C++ question, though. At least,
there is no standard C++ library function for that.

I'd hash {C1,C2,C3} as (C1*choose(80-C1,2) + hash {C2,C3})

HTH,
Michiel Salters

Yes that's exactly what I meant. And yes slightly off topic but c++ is my
native language and I generally find all the smart guys hang out in here. No
offense vb guys.

Thanks I will attempt that hash and if I read it correctly if c1,c2,c3 =
{1,2,3} then it'd be

(1* choose(80-1,2) + hash{ 2,3})

and hash would be passing 2,3 to my SuperFashHash function?

Thanks alot !!!

[Christian Gollwitzer]

Mi*************@tomtom.com wrote:

He knows all elements in advance, and furthermore, in his case he
probably
wants N==M.

In this case, it's off topic here. But to give some useful hint, this is
called "perfect hash" and there exist some tools, e.g. "gperf", to
create them (gperf generates C-code which hashes strings)

Christian