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Column-constrained categorical randomization (c0cat)

Source: R/c0cat.R
c0cat.Rd

c0cat() preserves the multiset of categories within each column but randomizes their positions across rows, leaving row margins free. This is the categorical analog to vegan's c0 algorithm. It is a non-sequential method.

Usage

c0cat(x, n_iter = 1L, output = c("category", "index"), seed = NULL)

Arguments

x

A matrix of categorical data, encoded as integers. Values should represent category or stratum membership for each cell.

n_iter

Number of iterations. Default is 1000. Larger values yield more thorough mixing. Ignored for non-sequential methods. Minimum burn-in times can be estimated with suggest_n_iter(). When row_groups or col_groups is used, n_iter iterations are run separately on every block. The number needed can be more or fewer than for the full matrix, so estimate it by passing the same groups to suggest_n_iter().

output

Character indicating type of result to return:

  • "category" (default) returns randomized matrix

  • "index" returns an index matrix describing where original entries (a.k.a. "tokens") moved. Useful mainly for testing, and for applications like quantize() that care about token tracking in addition to generic integer categories.

seed

Integer used to seed random number generator, for reproducibility.

Value

A matrix of the same dimensions as x, either randomized categorical values (when output = "category") or an integer index matrix describing the permutation of entries (when output = "index").

Examples

set.seed(123)
x <- matrix(sample(1:4, 100, replace = TRUE), nrow = 10)

# Randomize within columns (column margins fixed, row margins free)
x_rand <- c0cat(x)

# Verify columns are preserved but rows are not
all.equal(sort(x[, 1]), sort(x_rand[, 1]))
#> [1] TRUE
any(sort(x[1, ]) != sort(x_rand[1, ]))
#> [1] TRUE