Richard Goldstein and Martin Weiss have already pointed to -egen- and in
particular its -rowtotal()- function as the basis for a solution.
What is key to unpicking May's misunderstanding is realising that the
-sum()- function gives (cumulative) sums over observations, not
variables. In fact, that is stated in the online help.
May's intuition that a loop is needed is correct; it's just that -egen,
rowtotal()- does that loop for you.
Rowwise operations were reviewed more generally in
SJ-9-1 pr0046 . . . . . . . . . . . . . . . . . . . Speaking Stata:
Rowwise
(help rowsort, rowranks if installed) . . . . . . . . . . . N.
J. Cox
Q1/09 SJ 9(1):137--157
shows how to exploit functions, egen functions, and Mata
for working rowwise; rowsort and rowranks are introduced
Nick
[email protected]
May Baydoun, PhD
I have several variables that are mutually exclusive. In other words, if
one has a value, the others are missing. I want to sum them into a
single variable so that all observations have a value. They start with
the same few letters, say xyz but have different letters or numbers
thereafter.
I tried: gen newvar=sum(xyz*) but it didn't work out. Is there another
way to do this? I am guessing a loop?
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