The number of distinct `level_b` entries, e.g. peptides, within each `level_a` entry, e.g. protein.
Examples
istar <- prolfqua::sim_lfq_data_peptide_config()
#> creating sampleName from file_name column
#> completing cases
#> completing cases done
#> setup done
head(prolfqua:::nr_B_in_A(istar$data, "protein_Id", "peptide_Id"))
#> # A tibble: 6 × 2
#> protein_Id nr_peptide_Id_IN_protein_Id
#> <chr> <int>
#> 1 0EfVhX~0087 3
#> 2 7cbcrd~5725 1
#> 3 9VUkAq~4703 1
#> 4 BEJI92~5282 2
#> 5 CGzoYe~2147 1
#> 6 DoWup2~5896 1