Bernie,

Thanks for the tip, so it seems that I have to set the upper limit to 999
combinations. But, the below mentioned formula just gives the number of
posible combinations, but I also need the file described below. It is used
in modeling software which uses the first 50% for model building and the
second 50% for testing. Once I have all combinations written out I use
lookup functions to fill the values. So for the 4 points you describe below
it would look like this:

1 1
1 2
1 3
1 4
2 1
2 3
2 2
2 4
3 1
3 4
3 2
3 3

Can I easily produce such file with a threshold of max 999 combinations?
Regards,

Niels

"Bernie Deitrick" <deitbe @ consumer dot org wrote in message
...
Niels,

=COMBIN(#,#/2)/2

So, for 4 points, there are 3 unique splits:

1 2 3 4
1 3 2 4
1 4 2 3

unless order is important, then use

=COMBIN(#,#/2)

But note that there are
2.36x10^152
unique ways to split 512 points, so doubt you'll be able to deal with all
possible combinations.

HTH,
Bernie
MS Excel MVP


"Niels" wrote in message
...
For modeling purposes in need all posible combination to split 8-512
points in half (50% training, 50% testing). So for instance 10 points,
how many times can I make unique combinations of 5 by 5. The result file
should have in the fist column the number of the combination, and in the
second the order e.g.

1 1
1 2
1 3
1 4
1 5
1 6
1 7
1 8
1 9
1 10
2 10
2 1
2 2
2 3
2 4
2 5
2 6
2 7
2 8
2 9
3
.
etc. till max. 999

Any help is appreciated, regards,

Niels