Benjamin Klaus <[email protected]> writes,
> I want to export the (changing) content of a matrix "x" from mata into
> textfiles named "mi.txt", where "i" is a global macro. This should work in
> the following way, but it seems that the value of the global macro is not
> changed correctly at each stage of the loop...
>
>
> mata
> x = (76, 53, 48 \ 53, 88, 46 \ 48, 46, 63)
> i=0
> while (i<=5) {
>
> i = i + 1
> st_global("i",strofreal(i))
> stata("display($i)") // just to check the value
> // (it doesn't work)
> mm_outsheet("D:\m$i.txt", strofreal(x), "replace")
> }
> end
First let me address the problem asked about, and then let me give a better
way to proceed. Let's simplify the above to read
mata
i = 0
while (i<=5) {
i = i + 1
st_global("i", strofreal(i))
stata("display $i")
}
As Benjamin notes, it does not work: It displays nothing. What will work is
changing
stata("display $i")
to
stata("display $" + "i")
What was happening is that, at compile time -- at the time the lines were
entered into Mata, the contents of $i were substituted, so -stata("display $i")-
became -stata("display ")-. The way I just coded it, $ and i do not appear
adjacent yet, at execution time, the string "display $i" is assembled and
then that is substituted when it goes to Stata.
Now let's talk about mm_outsheet("D:\m$i.txt", strofreal(x), "replace").
Obviously, there is the issue of $i, and so the line could be replaced
with
mm_outsheet("D:\m$"+"i.txt", strofreal(x), "replace")
There still may be aproblem, however, depending on what mm_outsheet()
does with its first argument. I am not familiar with the function
-mm_outsheet()-, but understand, Mata at execution time does NOT substitute
macros. "$i" just means "$i". The reason -stata(display $" + "i")- worked
is that -display $i- was passed to Stata, and Stata expanded the macro $i.
Mata expands macros at compile time, but not at execution time.
One solution would be to use -st_macroexpand()-, the Mata function that
expands macros:
mm_outsheet(st_macroexpand("D:\m$"+"i.txt"), strofreal(x), "replace")
That would work, but it is not the solution I am recommending.
At this point, Benjamin must be thinking that working with macros in Mata is
mighty inconvenient. He would be right. Macros, so natural in Stata, are
not natural in Mata and in fact are not necessary. The better way to
code the problem would be,
i = 0
while (i<=5) {
i = i + 1
mm_outsheet("D:\m"+strofreal(i)+".txt", strofreal(x), "replace")
}
We might also use -for- rather than while,
for (i=1; i<=5; i++) {
mm_outsheet("D:\m"+strofreal(i)+".txt", strofreal(x), "replace")
}
and perhaps the code would be more easily read if we coded,
for (i=1; i<=5; i++) {
fn = "D:\m" + strofreal(i) + ".txt"
mm_outsheet(fn, strofreal(x), "replace")
}
or
for (i=1; i<=5; i++) {
fn = sprintf("D:\m%g.txt", i)
mm_outsheet(fn, strofreal(x), "replace")
}
-- Bill
[email protected]
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