Reading the first in every set of values in a column

[dvtarasov]

I have a matrix (let's call it D) with 20 rows (+ column name) and 2 columns. The matrix has been sorted in a particular way, and I want to read the first of every 4 values in the the first column to another matrix. The following code worked on a small "test" dataset (small enough that I could check the results manually), but is there a reason it could produce wrong results (for example, read a number twice from a particular set of four, but zero times from another set)?

proc iml;

use sasdata.testnum;

read all var _ALL_ into D[colname = varNames];

close sasdata.testnum;

print D;

T = j(5, 1, 0);

t_row = 1;

do y = 1 to 21 by 4;

    T[t_row, 1] = D[y, 1];

t_row = t_row + 1;

print T;

end;

In other words, does anyone see anything wrong with this code? Is there a better way of doing what I have done here?

[kannand]

Have you considered using the var _n_ along with a divisibility function I believe it is called MODZ () ??

[Rick_SAS · Accepted solution]

Use this. It uses the DO function to generate the sequewnce {1, 5, 9,...}:

t_row = do(1, nrow(D), 4);
T = D[t_row, 1];