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Re: st: Mata

From   [email protected] (William Gould, StataCorp LP)
To   [email protected]
Subject   Re: st: Mata
Date   Wed, 23 Jan 2008 08:12:41 -0600

Raphael Fraser <[email protected]> wrote, 

> Can anyone explain why the matrix X gives the incorrect result?
> [...]
> At some point the matrix F becomes A. What's the problem?

and Jeper Hansen <[email protected]> replied, 

> A view is what is says: a view.
> When you -insheet- data the second time, F is updated, and you get F
> == A. Is this the "problem" you are refering to? Maybe in this case
> you need -st_data()- instead of -st_view()?

Exactly right.  I would just like to add to that how Raphael can 
obtain the desire he wants:  use -st_data()- rather than -st_view()-
to create the first matrix.  Change the line that read 

        st_view(F=., ., .)

to read 

        F = st_data(., .)

so that the code becomes

        mata clear
        stata("insheet using freq.csv, clear")
        stata("drop subjectid")
        F = st_data(., .)                       // <- changed

        stata("insheet using amt.csv, clear")
        stata("drop subjectid")
        st_view(A=., ., .)
        X = 0.01*(A:*F)

st_data() makes a copy of the data in F.  st_view() makes F into a
view onto the data currently in memory.

-- Bill
[email protected]
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