st: merging on same using dataset

["Munro, Cameron" <munro@rand.org>]

I'm building up a choice dataset where I need to read in the characteristics of the alternatives for each individual. A simplified example of what I want to happen:
Master data -
Indiv    Choice
1        2 
2        4
...      ...

Using data -
Choice  x1   x2 ...
1       10   12
2       14   13
3       17   18
4       43   13
5       12   15

Desired output -
Indiv  Choice  x1  x2  _merge
1      1       10  12     2
1      2       14  13     3
1      3       17  18     2
1      4       43  13     2
1      5       12  15     2
2      1       10  12     2
2      2       14  13     2
2      3       17  18     2
2      4       43  13     3
2      5       12  15     2

In effect, what I want to do is merge sequentially down each observation in the master dataset in turn. The only way I can achieve this at the moment is to create separate files for each obs and then append them together after running the merge on each separately. But this results in many files, and is slow. Is there a better way?

Cheers

Cameron.

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