Extract elements of matrix

[James Harrigan]

I am writing code which performs a matrix calculation, generates a matrix result A, and then I want to put the elements of A into variables (or scalars, or locals).

To illustrate, the matrix A = [2 5 6], and has column names A1 A2 A3. The issue is that I am unable to use column names to extract the desired elements, as the following illustrates:

. mat list A

A[1,3]
A1 A2 A3
r1 2 5 6

. di A[1,2]
5

. di A[1,A2]
A2 not found
r(111);

. di A[1,"A2"]
matrix operators that return matrices not allowed in this context
r(509);

What am I doing wrong?

[Andrew Musau]

What version of Stata do you have? In Stata 16, the following is possible:

mat A = [2,5,6]
mat colnames A = "A1" "A2" "A3"
di A[1,"A2"]

Res.:

. mat A = [2,5,6]

. 
. mat colnames A = "A1" "A2" "A3"

. 
. di A[1,"A2"]
5

[James Harrigan]

Thanks for the response, Andrew. Your code is exactly what I'm trying to get working. I'm using version 14.2, from 2018, and it hadn't occurred to me that such a basic bit of syntax would be a new innovation.

[Andrew Musau]

Back then you needed the rownumb() and colnumb() functions to explicitly refer to the row name and column name, respectively. Something like:

mat A = [2,5,6]
mat colnames A = "A1" "A2" "A3"
di A[1,colnumb(A, "A2")]

Res.:

. mat A = [2,5,6]

. 
. mat colnames A = "A1" "A2" "A3"

. 
. di A[1,colnumb(A, "A2")]
5

[James Harrigan]

you're my savior Andrew, thanks! I try to avoid shelling out for every new version of Stata (I've been using it since version 1.3 in the late 1980s), but I guess might have to pony up for v16.