locating the coordinates (row,column) for a specific (string)

[Abhimanyu Arora]

Dear Statalist

I would like to search a string "1" (stored as string) in the matrix transcribed to mata from stata. Moreover, I would like to search it row-wise and increment the column no. in the loop. The reason is that I would like to get the first row where "1" occurs (in any column).

The following is my code. Can I request your help in understanding what is the mistake here and how to get the desired output?

mata
x=st_sdata(.,.)
for(i=1;i<=rows(x);i++){
for(j=1;j<=cols(x);j++){
if(x[i,j]=="1") break
printf("i=%g\n",i)
printf("j=%g\n",j)
}
}
i
j
end

Thanks
Abhimanyu

[Niels Henrik Bruun]

Hi

I would use -regexm- and matrix notation.

First example data:

: rseed(123)
: x = strofreal(runiformint(10,5,0,20))
: x
         1    2    3    4    5
     +--------------------------+
   1 |  10   17    6    6    9  |
   2 |  15    8   18    1   17  |
   3 |  20   19   10    3    5  |
   4 |   1   18    9    0   16  |
   5 |  19   14    0    1   12  |
   6 |   7    0   17    5    8  |
   7 |   4   20    3   13   12  |
   8 |   0   18   20   13   16  |
   9 |  17    3   12   10    4  |
  10 |  11   17   15   17    7  |
     +--------------------------+

Then the positions of ones can be found by -regexm-

: one_positions = regexm(x, "^1$")
: one_positions
        1   2   3   4   5
     +---------------------+
   1 |  0   0   0   0   0  |
   2 |  0   0   0   1   0  |
   3 |  0   0   0   0   0  |
   4 |  1   0   0   0   0  |
   5 |  0   0   0   1   0  |
   6 |  0   0   0   0   0  |
   7 |  0   0   0   0   0  |
   8 |  0   0   0   0   0  |
   9 |  0   0   0   0   0  |
  10 |  0   0   0   0   0  |
     +---------------------+

To get first row I utilize that undefined (dot) is plus infinity

: i = colmin((1::rows(x)) :/ (rowsum(one_positions) :> 0))
: i
  2

And to get column position

: j = rowmin((1..cols(x)) :/ (one_positions[i,.] :> 0))
: j
  4

In your code you need to break twice, eg like (note how I run through the j's):

: for(i=1;i<=rows(x);i++){
>         for(j=1;j<cols(x);j++){
>                 if(x[i,j]=="1") break
>         }
>         if(x[i,j]=="1") break
> }
: i
  2
: j
  4

[Abhimanyu Arora]

Thanks very much indeed, Neils, both for the alternative method and improving the earlier code.
Cheers
Abhimanyu