Add Interaction Contrasts to an msreve_design — add_interaction

Creates new contrast columns representing pairwise interactions of existing contrasts in an msreve_design object. Interactions are computed as element-wise products of the contrast vectors.

Usage

add_interaction_contrasts(design, pairs = NULL, orthogonalize = TRUE)

Arguments

design: An object of class msreve_design.
pairs: Optional two-column matrix or list of character vectors specifying pairs of contrast column names. Default NULL uses all pairwise combinations.
orthogonalize: Logical; if TRUE (default) the expanded contrast matrix is passed through orthogonalize_contrasts.

Value

The updated msreve_design object with non-zero interaction columns appended. Zero interactions are automatically skipped.

Details

Interaction contrasts are created by element-wise multiplication of pairs of contrast vectors. If the resulting interaction is a zero vector (which occurs when the original contrasts have non-overlapping support, i.e., no conditions where both contrasts are non-zero), the interaction is skipped with an informative message. This commonly happens with contrasts that compare distinct subsets of conditions, such as c(1,-1,0,0) and c(0,0,1,-1).

Examples

if (FALSE) { # \dontrun{
# Example with non-overlapping contrasts (zero interaction)
C1 <- matrix(c(1,-1,0,0, 0,0,1,-1), nrow=4, 
             dimnames=list(NULL, c("A","B")))
# A compares conditions 1 vs 2, B compares 3 vs 4
# Their interaction will be zero and skipped

# Example with overlapping contrasts (non-zero interaction)  
C2 <- matrix(c(1,1,-1,-1, 1,-1,1,-1), nrow=4,
             dimnames=list(NULL, c("Main1","Main2")))
# These contrasts overlap and will produce a meaningful interaction
} # }