Language Reference
COL Function
COL (x) ;
This function is supported by the IML procedure and the iml action.
The COL function is part of the IMLMLIB library. The COL function returns a matrix that has the same dimensions as the x matrix and whose jth column has the value j. You can use the COL and ROW function to extract elements of a matrix. For example, the following statements fill the subdiagonal, superdiagonal, and main diagonal of a matrix with a sequence of numbers:
x = j(5, 5, 0); /* allocate 5 x 5 matrix of zeros */
r = row(x); /* create helper matrices */
c = col(x);
idx = loc(abs(r-c)<= 1); /* indices of sub-, super-, and main diagonal */
x[idx] = 1:ncol(idx); /* fill with 1,2,3,... */
print x[format=Best3.];
Figure 74: A Tridiagonal Matrix
| x | ||||
|---|---|---|---|---|
| 1 | 2 | 0 | 0 | 0 |
| 3 | 4 | 5 | 0 | 0 |
| 0 | 6 | 7 | 8 | 0 |
| 0 | 0 | 9 | 10 | 11 |
| 0 | 0 | 0 | 12 | 13 |
If r = row(m) and c = col(m) are two matrices, then you can use logical comparisons of r and c to describe certain submatrices, such as in Table 2.
Table 2: Some Common Submatrices
| Submatrix | Index by LOC of |
|---|---|
| Diagonal | r = c |
| Upper triangular | r < c |
| Lower triangular | r > c |
| Banded with radius d | abs(r-c) <= d |
| Antidiagonal | r + c -1 = ncol(r) |
You can also use the COL function to generate an ID variable when you convert data from a wide format to a long format. For example, the following statements show how to generate a column vector with values 
:
NumSubjects = 5; /* number of subjects */
NumRepeated = 3; /* number of repeated obs per subject */
Y = col(j(NumSubjects, NumRepeated));
Repl = shape(Y, 0, 1); /* {1, 2, 3, 1, 2, 3, ..., 1, 2, 3} */