Many thanks for this. I will carefully look at it. It seems that this will
make the program much faster, which would be _very_ important. The snippet
will often run more than a million times ...
William Gould, Stata wrote:
> Ulrich Kohler <[email protected]> wrote,
>
> > I have a Mata function which looks as follows:
> >
> > -------------------------------------lsq.mata--
> > (...)
> > // Mata Function to extract the substitution costs from subcost-matrix
> > void showhash(real rowvector R)
> > {
> > string scalar key1
> > st_local("key1",key1)
> > key1 = strofreal(R[1,2])
> > st_local("key1",key1)
> > stata("local hash1 = mod(`key1',197)")
> > }
> >
> > (...)
> >------------------------------------------------
>
> and Uli notes that when he runs it, he gets an error,
>
> > : R = 2,3,5,4
> > : showhash(R)
> >
> > invalid syntax
> > stata(): 3598 Stata returned error
> > showhash(): - function returned error
> > <istmt>: - function returned error
> > r(3598);
>
> Alan Riley <[email protected]> has already given a solution, and suggested
> the line
>
> stata("local hash1 = mod(`key1',197)")
>
> be changed to read
>
> stata("local hash1 = mod(\`key1',197)")
>
> Alan's right, but his solution is too tricky for me. Moreover, his
> solution shows he is still thinking an ado mode rather than Mata mode.
>
> My suggested solution is
>
> stata("local hash1 = mod(" + key1 + ", 197)")
>
> and, with my solution, Uli's code can be simplified to read,
>
>
> void showhash(real rowvector R)
> {
> string scalar key1
>
> key1 = strofreal(R[1,2])
> stata("local hash1 = mod(" + key1 + ", 197)")
> }
>
> or even
>
> void showhash(real rowvector R)
> {
> stata("local hash1 = mod(" + strofreal(R[1,2]) + ",
> 197)") }
>
> Let me expound on the ado versus the Mata way of thinking.
>
> Uli wanted to run the Stata command
>
> local hash1 = mod(_______, 197)
>
> where he substituted the value from Mata matrix R[1,2] for ______.
> Why Uli wanted to do this, we don't know, nor care.
>
> The ado way of thinking says we substitute a macro for _____, and arrange
> for the macro to contain R[1,2], so when the macro is substituted by
> Stata, we obtrain the desired result. Good way of thinking, when you
> are writing an ado-file.
>
> The Mata way of thinking is more direct: we need to construct a string
>
> "local hash1 = mod(_______, 197)"
>
> where where R[1,2] is substitued for _____, and we can just use the
> standard operators to do that,
>
> "local hash1 = mod(" + strofreal(R[1,2]) + ", 197)"
>
> Here's a good rule: It's perfectly okay to obtain input from macros, or
> post output to macros. That is one way Mata can communicate with
> ado-files. If you have to use macros to obtain your result, however, you
> are thinking ado, not Mata. There's a simpler, more direct way.
>
> -- Bill
> [email protected]
> *
> * For searches and help try:
> * http://www.stata.com/support/faqs/res/findit.html
> * http://www.stata.com/support/statalist/faq
> * http://www.ats.ucla.edu/stat/stata/
--
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+49 (030) 25491-361
*
* For searches and help try:
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* http://www.ats.ucla.edu/stat/stata/
