A numeric matrix read from a labelled TSV: an empty top-left cell, then
column IDs as the header, then one row per sample (row ID + tab-separated
values). Used for both the response (samples × species) and the constraint
(samples × variables) tables.
Result of a Redundancy Analysis. Eigenvalues, proportion explained, and the
site/species scores plus biplot and site-constraint scores follow
skbio.stats.ordination.rda. The first n_constrained axes are canonical
(constrained by the explanatory variables); the rest are the unconstrained
PCA of the residuals.