Explain why a matchup contrast is not well defined

Produces a human-readable message for a contrast rejected by valid_contrast(), for use in error messages or interactive UIs.

Usage

contrast_message(A, B)

Arguments

A, B

Named lists mapping attribute stems to pinned levels.

Value

A length-1 character string.

See also

valid_contrast()

Examples

contrast_message(list(party = "R"), list(party = "R"))
#> [1] "Candidates A and B are identical on: party. A clean comparison needs them to differ on a shared attribute, e.g. A: party = Republican vs B: party = Democrat. As specified, the matchup compares identical profiles and reflects which position was shown first, not a real difference."