st: Generate variables being as the difference between two varlists

[Robert Maderitsch <r.maderitsch@googlemail.com>]

Dear Statalisters,
I have the following problem:

The data looks like this:

a1      a2      a3      b1     b2      b3
1        3        3        2        2        3
2        4        2        3        2        5
3        5        1        5        3        2

Now I want to generate new variables as
c1=b1-a1
c2=b2-a2
c3=b3-a3

However, as my dataset is really big, I want to automate this.
I tried for example a double loop:

foreach x in a1-a3 {
foreach y in b1-b3 {
gen c1_`x'_`y'=`y'-`x'
}
}

The problem with this is, however, that this generates 9 new variables
(for all possible combinations) and this is not what I want.
There must be easier solutions.
Does anyone have a suggestion?

Thank you very much!
Robert

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