Read the declaration a joint exposure carries

These three functions read back what joint_exposure() recorded, so that a package holding a column of exposures can act on the crossing without rebuilding it.

is_joint_exposure() reports whether an object declares a crossing. joint_components() reports which two treatments were crossed and the levels each of them takes. joint_reference() reports the cell the effects are reported against.

Usage

is_joint_exposure(x)

joint_components(x)

joint_reference(x)

Arguments

x

A joint exposure, as built by joint_exposure(). is_joint_exposure() accepts any object.

Value

is_joint_exposure() returns a single TRUE or FALSE. joint_components() returns a named list of two character vectors, one per component, named for the treatments. joint_reference() returns the reference cell's label as a single string.

Details

They are plain functions rather than generics. The declaration lives in the attributes of one class, and a package that meets a joint exposure needs the same answer this package would give rather than a place to register a different one.

joint_components() gives the component names in the order the crossing was declared in, and each component's levels in the order the crossing varies them, which is the order that settles the cell labels. joint_reference() gives the first level of the vector, which is the cell crossing the two components' reference levels.

See also

joint_exposure(), which records what these read back.

Examples

x <- joint_exposure(
  qsmk = c(0, 1, 0, 1),
  exercise = c("no", "no", "yes", "yes")
)

is_joint_exposure(x)
#> [1] TRUE
joint_components(x)
#> $qsmk
#> [1] "0" "1"
#> 
#> $exercise
#> [1] "no"  "yes"
#> 
joint_reference(x)
#> [1] "qsmk = 0, exercise = no"