M Hollis wrote:
> --- "William Gould, Stata" <[email protected]> wrote:
> > My suggested solution is
> >
> > stata("local hash1 = mod(" + key1 + ", 197)")
>
> Thanks for your detailed discussion about mata vs. ado
> files. Very helpful. I was wondering, though, if you
> could provide a manual reference or more of a
> description of the syntax in your suggested solution
> above. In particular, I'm wondering what the " + key1
> + " is doing exactly. I haven't run across that
> option in the manual, and it's hard to search the help
> for something that's just quotes and plus signs. I
> feel like it could be a very useful function if I
> could figure out how it works.
Not that I am competent, but I think I can answer your question partly. Bill
might step in to correct me if I were wrong.
In general, you have to put a string within the parentheses of stata(), hence
you have to state:
: stata("local hash1 = mod(1,197)")
Now, consider the situation that you want to change the code to something
saying
: stata("local hash1 = mod(x,y)")
where x and y are Mata variables. As it stands x and y not get "expanded",
because they are enclosed in quotes. Hence Stata would see
-local hash1 = mod(x,y)- which will give an error. Bills trickery now is to
close the quotation before x, than plug in x as a Mata Function, and finally
put the rest of the command in quotes again. Hence is code should read as
: stata(
"local has1 = mod" // <- within qoutes
x // <- without qoutes
", " // <- within qoutes
y // <- without qoutes
")" // <- within quotes
)
But that is only the first part of the idea. The second part is, that x and y
has to be "enclosed" between + signs.
: stata(
"local has1 = mod"
+ x + // <- within +
", "
+ y + // <- within +
")"
)
Don't ask me why, but it works ;-). Probably that way Mata knows that it has
to calculate something. Maybe someone else can take over for the explanation.
Uli
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