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

[Nick Cox <njcoxstata@gmail.com>]

Here are some other solutions.

(1)

Only for 0 and 1 is a number equal to its own square. Hence

: x = (0,0,0,0,1,1,1)

: x == x:^2
  1

A graph such as

twoway function x^2, ra(-3  3) || function x, ra(-3 3)

may help make this vivid.

(2)

 sum((x :== 0) :| (x :== 1)) == length(x)

Nick
njcoxstata@gmail.com

On 17 November 2013 05:30, Joseph Coveney <stajc2@gmail.com> wrote:
> 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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