An S3 class for representing information on massive SNP arrays.
A named list with at least 3 slots:
A FBM.code256 which is
a special Filebacked Big Matrix encoded with type raw (one byte
unsigned integer), representing genotype calls and possibly imputed
allele dosages. Rows are individuals and columns are SNPs.
A data.frame containing some information on the individuals
(read from a ".fam" file).
A data.frame giving some information on the variants
(read from a ".bim" file).