Internal constructor for projoint_data objects.
Used by reshape_projoint and make_projoint_data to
bundle conjoint survey labels and response data into a consistent structure.
projoint_data(labels, data)A list of length two with class "projoint_data", containing:
$labels: attribute–level mapping
$data: respondent–task–profile dataset
A data frame of conjoint attribute–level metadata. Must include
attribute names, attribute IDs (e.g., "att1"), and level IDs
(e.g., "att1:lev1").
A data frame (typically a tibble) containing the reshaped conjoint
survey responses, one row per respondent–task–profile, with attribute columns,
selected, agree, and any covariates.