So now the interaction for bivariate combinations is MUCH shorter! Thanks for implementing the operator!
In comparison to my function and the '^' operator result I noticed a slight difference:
Is it intended that the value in 'grrr_grr_2' is '4' and not '1'?

<hansl>
nulldata 10
matrix g1 = {1;1;1;1;1;1;2;2;2;2}
matrix g2 = {1;1;1;1;1;1;1;1;2;2}
matrix g3 = {1;1;2;2;2;3;3;3;4;4}
series gr = g1
series grr = g2
series grrr = g3
delete --type=matrix # no instantly update of symbols
list G1 = gr grr grrr
list part1 = null
list part2 = G1
list inter = null
loop foreach i G1 -q
part1 = G1.\$i
part2 -= G1.\$i
inter += part1^part2
endloop
<hansl>

Am 14.02.2013 11:48, schrieb Riccardo (Jack) Lucchetti:
On Thu, 14 Feb 2013, Pindar wrote:

Hi there,

I'd like to ask what the interaction operator 'makes'?

I was working on a function that generates new interaction series for each step combination of factors.
This is working for a list of factors and generates bivariate combinations as in A*B
I'm stuck with making it possible to generate A*B*C and so on.
This should be possible with a recursive function!
I think with a new gretl operato '*' the whole procedure would get much easier to implement.

I also encountered some bugs (at least on W8):
- having 'opened' a bundle and then using the '= null' command gretl crashes
- 'smpl full' does 'sometimes' not work in functions - I think if it's outside a loop.
- 'delete --type==' does not update the symbols window automatically

Here is the code for the function as well (gonna be implemented in my new multivariate statistic package).
Perhaps someone has an idea how to solve the sorting issue for more than A*B.

I've documented the new operator (warning: it's "^", not "*") in the CVS version of the manual not very long ago: in the A4 version (http://sourceforge.net/projects/gretl/files/manual/gretl-guide-a4.pdf/download) look for pages 91-92.

Anyway, the following script should give you a good idea:

<hansl>
open mroz87.gdt --quiet

# the coding below makes it so that
# KIDS = 0 -> no kids
# KIDS = 1 -> young kids only
# KIDS = 2 -> young or older kids

series KIDS = (KL6 > 0) + ((KL6 > 0) || (K618 > 0))

list D = CIT KIDS # interaction discrete variables
list X = WE WA    # variables to "split"
list INTER = D ^ X

smpl 1 6

print D X INTER -o
</hansl>

-------------------------------------------------------
Riccardo (Jack) Lucchetti
Dipartimento di Scienze Economiche e Sociali (DiSES)

Università Politecnica delle Marche
(formerly known as Università di Ancona)

r.lucchetti@univpm.it
http://www2.econ.univpm.it/servizi/hpp/lucchetti
-------------------------------------------------------