st: Re: How to determine if a variable is a dummy in mata

["Joseph Coveney" <stajc2@gmail.com>]

Paul Corral wrote:

I'm been trying to determine if a variable is a dummy or not within mata.

Is there an easy way to do this without iterating over each row of a
matrix's column and check if it is either 0 or 1. I was trying to use
the allof() command, however it can only check if all are a scalar.
So, while I may check if all are ones, it won't allow me to check if
all are 0 or 1.

--------------------------------------------------------------------------------

Something like that below should work.  If you don't like the verbosity, you can
condense it all to a single line of code, although it might make it difficult to
follow.

Other ways come to mind to accomplish the same thing, for example, to covert the
column to text and then use a string search (glance through Mata's string
functions for guidance) for characters other than "0" and "1".  Some of them
might be more efficient, too.

Joseph Coveney

: mata set matastrict on

: 
: real scalar function indicator(
>                 real matrix TestedMatrix, 
>                 real scalar tested_column_index) {
> 
>         real colvector TestedColumn
>         TestedColumn = TestedMatrix[., tested_column_index]
> 
>         TestedColumn = uniqrows(TestedColumn)
> 
>         real scalar result
>         result = (
>                 (TestedColumn[1] == 0) && 
>                 (TestedColumn[2] == 1) &&
>                 (rows(TestedColumn) == 2)
>                 )
> 
>                 return(result)
> }

: 
: A = (0, 1, 2, 3 \ 1, 4, 5, 6 \ 0, 7, 8, 9)

: 
: indicator(A, 1)
  1

: indicator(A, 2)
  0

: 
: A = A \ (10, 11, 12, 13)

: 
: indicator(A, 1)
  0

: 
: end

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