Create Covariate Combinations Across Groups

Description

This function generates all possible combinations of covariates by selecting one variable from each user-defined group. Groups can be defined either by a regular expression pattern (pattern) or by exact variable names (name). The resulting list can be input into the covariates argument in write_inla_formulas to generate multivariable model formulas where all combinations of covariates are needed.

cov_multi(covariates, pattern = NULL, name = NULL, add = FALSE)

Arguments

  • covariates: A character vector or a list of single-element character vectors. Typically obtained from extract_names or cov_uni or cov_nl.
  • pattern: A character vector of regular expression patterns (e.g., “tmin” matches “tmin”, “tmin.l1”, etc.). Each pattern defines a group to draw covariates from.
  • name: A character vector of exact variable names to include as an additional group.
  • add: Logical; if TRUE, appends the generated combinations to the original covariates object. Default is FALSE.

Returns

A list of character vectors. Each element is a unique combination of covariates, where one variable is drawn from each specified group. The resulting list is suitable as input in the covariates argument in write_inla_formulas.

Examples

data <- data.frame(tmin = rnorm(10), tmin.l1 = rnorm(10),
                   pdsi = rnorm(10), urban = rnorm(10))

# Extract covariate names
covs <- extract_names(data, pattern = c("tmin", "pdsi", "urban"))

# Combine "tmin" and "pdsi" into all possible pairings
cov_multi(covariates = covs, pattern = c("tmin", "pdsi"))

# Combine "tmin" and "urban", treating "urban" as an exact match
cov_multi(covariates = covs, pattern = "tmin", name = "urban")

# Use output as input to write_inla_formulas()
combined_covs <- cov_multi(covariates = covs, pattern = c("tmin", "pdsi"))
formulas <- write_inla_formulas(outcome = "cases", covariates = combined_covs)