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

[Nick Cox <njcoxstata@gmail.com>]

Compared with your original question, being able to check Stata
variables for being dummy (indicator) within Stata appears to be of
interest here.

Given -findname- (SJ)

findname, all(inlist(@, 0, 1))

finds all dummy variables and leaves their names in r(varlist).
Without -findname-, this would work:

local dummies

foreach v of var * {
    capture assert `v' == 0 | `v' == 1
    if _rc == 0 local dummies `dummies'  `v'
}

If missings are possible, logical tests should be modified appropriately

You appear to add an extra condition, that both values of 0 and 1
occur at least once. That's not part of the definition and wasn't part
of your original question. There are various ways of tackling that.
Here is one:

local dummies

foreach v of var * {
    capture assert `v' == 0 | `v' == 1
    if _rc == 0 {
                su `v', meanonly
                if r(mean) > 0 & r(mean) < 1 local dummies `dummies'  `v'
}

Nick
njcoxstata@gmail.com


On 17 November 2013 16:34, Paul Corral <paul.corral@gmail.com> wrote:
> Thank you for the help. I ended up doing the following:
>
> local words=wordcount("`vars'")
> matrix dummy=J(1,`words',0)
>
> tokenize `vars'
>
> forvalues x= 1/`words'{
>
> capture assert ``x''==1 | ``x''==0
> if  _rc==0 {
> qui: tab ``x''
> if r(r)==2{
> matrix dummy[1,`x']=1
> }
> }
> }
> Then once in mata I just imported that matrix using st_matrix.

> On Sun, Nov 17, 2013 at 6:01 AM, Nick Cox <njcoxstata@gmail.com> wrote:
>> (2) better as
>>
>> : all((x :== 0) :| (x :== 1))
>> Nick
>> njcoxstata@gmail.com
>>
>>
>> On 17 November 2013 10:09, Nick Cox <njcoxstata@gmail.com> wrote:
>>> 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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