Add empty columns for auxiliary features.
Examples
n <- 5
p <- 10
x <- matrix(data = rnorm(n * p), nrow = n, ncol = p)
primary <- as.logical(rbinom(n = p, size = 1, prob = 0.5))
x_primary <- x[, primary]
x_expanded <- corila:::.expand_auxiliary(x = x_primary, primary = primary)
all(x_expanded[, primary] == x[, primary])
#> [1] TRUE
all(x_expanded[, !primary] == 0)
#> [1] TRUE