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RE: st: Appending several files
Thanks, Nick, for your comments and your alternative suggestion.
At 08:01 AM 10/16/2006, you wrote:
[...]
2. As you want the numeric interpretation, I find
local j = 0
clearer, particularly as you are testing its
numeric value later. Stata doesn't care, but
a code reader might.
Yes, indeed, but we are also told, understandably, that
local j "0"
is more efficient. But it is a minor inconvenience for Stata to
process -local j = 0-. Furthermore, if I had been really attentive
to the fact the j is a number, then I would have used scalars
instead. But I use macros to make use of the ++ operator. I don't
believe that it applies to scalars. (??)
3. If you are a Windows user and accustomed
to putting spaces in your filenames, this will
fall over unless the names come quoted.
Yes, indeed. But I am not one to use spaces in file names, so I
hadn't thought of that. (I find them a bit of an anathema. But they
are with us now, at least among Windows users, and there's no turning
back. I suppose they are a feature that was created to make computers
more accessible to the Muggles.)
I feel queasy about going through two loops
simultaneously unless it's unavoidable.
That's mostly just a style prejudice.
[...]
I hadn't even thought of it as two loops simultaneously. I think of
it as one loop with f as the driver; j is a "passenger". It is not
unusual, in general programming, to have many "passenger" variables
in a loop, each acquiring new values in each iteration.
Another matter: I used the "number" j as a convenient way to tell
whether you are in the first iteration. You don't really need to know
the iteration count; the real issue is whether the loop is in the
first iteration. Thus you can do:
local first = 1
foreach f in `r(files)' {
if `first' {
use `f'
local first = 0
}
else {
append using `f'
}
Also, Paul Seed had another interesting technique.
--David
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