mgcv (version 1.8-16)

uniquecombs: find the unique rows in a matrix

Description

This routine returns a matrix or data frame containing all the unique rows of the matrix or data frame supplied as its argument. That is, all the duplicate rows are stripped out. Note that the ordering of the rows on exit need not be the same as on entry. It also returns an index attribute for relating the result back to the original matrix.

Usage

uniquecombs(x,ordered=FALSE)

Arguments

x

is an R matrix (numeric), or data frame.

ordered

set to TRUE to have the rows of the returned object in the same order regardless of input ordering.

Value

A matrix or data frame consisting of the unique rows of x (in arbitrary order).The matrix or data frame has an "index" attribute. index[i] gives the row of the returned matrix that contains row i of the original matrix.

Details

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.

When x has only one column then the routine uses unique and match to get the index. When there are multiple columns then it uses paste0 to produce labels for each row, which should be unique if the row is unique. Then unique and match can be used as in the single column case. Obviously the pasting is inefficient, but still quicker for large n than the C based code that used to be called by this routine, which had O(nlog(n)) cost. In principle a hash table based solution in C would be only O(n) and much quicker in the multicolumn case. unique and duplicated, can be used in place of this, if the full index is not needed. Relative performance is variable.

If x is not a matrix or data frame on entry then an attmept is made to coerce it to a data frame.

See Also

unique, duplicated, match.

Examples

require(mgcv)

## matrix example...
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 Xu
Xu[ind[3],];X[3,]

## same with fixed output ordering
Xu <- uniquecombs(X,TRUE);Xu
ind <- attr(Xu,"index")
## find the value for row 3 of the original from Xu
Xu[ind[3],];X[3,]


## data frame example...
df <- data.frame(f=factor(c("er",3,"b","er",3,3,1,2,"b")),
      x=c(.5,1,1.4,.5,1,.6,4,3,1.7))
uniquecombs(df)