Danielle H. Ferry
>
> Suppose I want to create 2 temporary datasets inside a
> -forval- loop, with
> names indexed by the loop number (i.e., `results0',
> `results1'). Once I get
> outside the loop, I want to append them using -dsconcat-,
> but since I
> defined them inside the loop, they no longer exist.
>
> A more concrete example:
>
> forval k = 0(1)1 {
>
> tempname memhold
> tempfile results
>
> postfile `memhold' var1 var2 var3 using `results'`k', replace
>
> forval y = 1998(1)2002 {
> ...
>
> post `memhold' (`x') (`y') (`z')
> }
>
> postclose `memhold'
> }
>
> dsconcat `results0' `results1'
>
This issue arises from a misunderstanding
of how local macros are defined.
If I go
. tempfile results
Stata opens up a file for writing. In my
case if I have a look I find that's a file
in an appropriate directory with a name like
ST_05000001.tmp
Your name will differ, but it will be of
similar form, I imagine, modulo any style
difference dependent on platform. That is, the local
macro -results- will contain something like
<path leading to>/ST_05000001.tmp
Now suppose I have local macro -k-
and I refer to
`results'`k'
and -k- is variously (to follow your example)
0 and 1.
Stata will read this as variously
<path leading to>/ST_05000001.tmp0
and
<path leading to>/ST_05000001.tmp1
which happen to be legal filenames
as far as my platform is concerned,
so I imagine there will be no problem
yet as far as Stata is concerned.
(N.B. this is a guess.)
Later you refer to local macros
`results0', `results1'. However,
you never defined these macros,
so they are interpreted as empty;
and I imagine that -dsconcat- complains
at some point, given it is, from
its point of view, supplied with no
information.
To put the matter another way, forget
about filenames: the fallacy here
is presuming that
`a'`b'
is the same as
`a`b''
It could be the same in practice,
but in principle these are quite different
things. Indeed, `a' and `b' could both
exist, yet `a`b'' could not exist at
all.
1. `a'`b'
=========
`a'`b' is interpreted this way. Stata sees
`a', substitutes the contents of local macro
-a- (meaning, nothing if that does not
exist); similarly with `b'. The result
is concatenation of the contents of two
macros, treated as strings.
2. `a`b''
=========
`a`b'' is interpreted this way. Stata sees
nested macro names, so works from the
inside outwards, just as with parentheses
in elementary mathematics. Again the
same principle applies: if one or both
of the macro names don't exist, then
the result will be an empty string.
After all that explanation, a fix is relatively easy,
although I haven't tested this:
forval k = 0/1 {
tempname memhold
tempfile results`k'
postfile `memhold' var1 var2 var3 using `results`k'', replace
forval y = 1998(1)2002 {
...
post `memhold' (`x') (`y') (`z')
}
postclose `memhold'
}
dsconcat `results0' `results1'
However that generalises awkwardly. Suppose you wanted
to do this for 42 values:
forval k = 0/41 {
tempname memhold
tempfile new
local files `"`files'"`new'" "'
postfile `memhold' var1 var2 var3 using `new', replace
forval y = 1998(1)2002 {
...
post `memhold' (`x') (`y') (`z')
}
postclose `memhold'
}
dsconcat `files'
Be clear what is happening here. As Stata goes
round the loop, every time it meets
tempfile new
It opens a _new_ file with a new _real_ name.
That is, the meaning of the local macro -new-
changes. So, depending on what else is going,
it might well be, in succession,
<path leading to>/ST_05000001.tmp
<path leading to>/ST_05000002.tmp
<path leading to>/ST_05000003.tmp
and so forth. All this is no problem,
as long as you keep a list of the files,
adding the names as they are created.
Nick
[email protected]
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