This routine returns a matrix containing all the unique rows of the
matrix supplied as its argument. That is, all the duplicate rows are
stripped out. Note that the ordering of the rows on exit is not the same
as on entry. It also returns an index attribute for relating the result back
to the original matrix.
Usage
uniquecombs(x)
Value
A matrix consisting of the unique rows of x (in arbitrary order).
The matrix has an "index" attribute. index[i] gives the row of the returned
matrix that contains row i of the original matrix.
Models with more parameters than unique combinations of
covariates are not identifiable. This routine provides a means of
evaluating the number of unique combinations of covariates in a
model. The routine calls compiled C code.
See Also
unique can do the same thing, including for
non-numeric matrices, but more slowly and without returning the
index.
X<-matrix(c(1,2,3,1,2,3,4,5,6,1,3,2,4,5,6,1,1,1),6,3,byrow=TRUE)
print(X)
Xu <- uniquecombs(X);Xu
ind <- attr(Xu,"index")
## find the value for row 3 of the original from XuXu[ind[3],];X[3,]