Re: st: matrix references with column names

[Stas Kolenikov <skolenik@gmail.com>]

You can get the row/column numbers with colnumb(b,"age") and
rownumb(b,"age") functions. The code looks cumbersome, but it works.
You can break this down for readability into

local whereagecol = colnumb(b,"age")
local whereagerow = colnumb(b,"age")
disp b[`whereagerow',`whereagecol']


-- Stas Kolenikov, PhD, PStat (ASA, SSC)
-- Senior Survey Statistician, Abt SRBI
-- Opinions stated in this email are mine only, and do not reflect the
position of my employer
-- http://stas.kolenikov.name



On Tue, Sep 17, 2013 at 1:14 PM, David Kantor <kantor.d@att.net> wrote:
> Hello,
>
> Suppose I have a matrix b, I want to refer to a single element using the row
> and column names:
> b["age", "age"]
>
> This seems to be okay for defining a 1x1 matrix, as in,
> mat c = b["age", "age"]
>
> But it is not okay when I want refer to it as a scalar quantity, such as
> disp b["age", "age"]
> or
> scalar q = b["age", "age"]
>
> ; I get the error:
> "matrix operators that return matrices not allowed in this context"
>
> But in these contexts, it okay to refer to refer to elements by number:
> disp b[2,2]
>
> So, to refer to an element by row and column names, I seem to be forced to
> extract a copy:
> mat c = b["age", "age"]
> disp c[1,1]
>
> Is there a better way to do this?
> I can imagine searching in the rownames and colnames for the corresponding
> indices, but that's a lot of work; it ought to be easier than that.
>
> I am using Stata 10. Has this changed in Stata 13?
>
> I note that in my documentation, in [U]14.9, there is an example:
> generate sdif - dif / sqrt(V["price", "price"])
>
> which can be expected to fail.
>
> Thanks if anyone can help with this.
> --David
>
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