Internal function that detects missing model x target combinations by comparing observed data against the complete grid of all compare-column values crossed with all observed target combinations.
build_missing_grid(scores, compare = "model")A data.table with forecast-unit columns for each
missing combination. Zero rows if nothing is missing.
A scores object (data.table with a metrics
attribute as produced by score()).
Character string (default "model") naming the
column whose values are compared against each target.