st: Combinations of 3

[Kari Hexem <khexem@gmail.com>]

Hi,

I would like to sum the numbers of variable v with 6 other variables:
n1, n2, n3, n4, n5, n6,
in combinations of 3.  So the results would be the sums of the
following variables,
identified using 15 combinations (6 choose 2), or, to spell it out,
the sums of each of these
following possibilities:
v-n1-n2
v-n1-n3
v-n1-n4
v-n1-n5
v-n1-n6
v-n2-n3
v-n2-n4
v-n2-n5
v-n2-n6
v-n3-n4
v-n3-n5
v-n3-n6
v-n4-n5
v-n4-n6
v-n5-n6

I can get the sum of the first two of the 3 variables by using the
following code:
forvalues i=1(1)6 {
  gen sum`i' = v + n`i'
}

but I can't figure out how to add in the 3d variable, which can't be a
repeat of the 2nd variable (ie. v-n1-n1 is not allowed).  Thoughts?  I
feel like it should have something to do with nested loops, or the
-selectvars- command, but I am totally stuck.  Any help would be
greatly appreciated.

Thanks,
Kari
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