Duplicated columns in dummy matrix

The algorithm is based on crossprod(x) or crossprod(x, u) where u is a vector of random numbers

Usage

DummyDuplicated(x, idx = FALSE, rows = FALSE, rnd = FALSE)

Arguments

x

A matrix

idx

Indices returned when TRUE

rows

Duplicated rows instead when TRUE

rnd

Algorithm based on cross product with random numbers when TRUE (dummy matrix not required)

Value

Logical vectors specifying duplicated columns or vector of indices (first match)

Details

The efficiency of the default algorithm depends on the sparsity of crossprod(x). The random values are generated locally within the function without affecting the random value stream in R.

Author

Øyvind Langsrud

Examples

x <- cbind(1, rbind(diag(2), diag(2)), diag(4)[, 1:2])
z <- Matrix(x[c(1:4, 2:3), c(1, 2, 1:5, 5, 2)])

DummyDuplicated(z)
#> [1] FALSE FALSE  TRUE  TRUE FALSE FALSE FALSE  TRUE  TRUE
which(DummyDuplicated(z, rows = TRUE))
#> [1] 5 6

# Four ways to obtain the same result
DummyDuplicated(z, idx = TRUE)
#> [1] 1 2 1 2 5 6 7 7 2
DummyDuplicated(z, idx = TRUE, rnd = TRUE)
#> [1] 1 2 1 2 5 6 7 7 2
DummyDuplicated(t(z), idx = TRUE, rows = TRUE)
#> [1] 1 2 1 2 5 6 7 7 2
DummyDuplicated(t(z), idx = TRUE, rows = TRUE, rnd = TRUE)
#> [1] 1 2 1 2 5 6 7 7 2

# The unique values in four ways 
which(!DummyDuplicated(z), )
#> [1] 1 2 5 6 7
which(!DummyDuplicated(z, rnd = TRUE))
#> [1] 1 2 5 6 7
which(!DummyDuplicated(t(z), rows = TRUE))
#> [1] 1 2 5 6 7
which(!DummyDuplicated(t(z), rows = TRUE, rnd = TRUE))
#> [1] 1 2 5 6 7