Treat multiple sequences as a array where each row corresponds to a sequence for one species.
# S3 method for ms
[(x, rows)An object of type ms
A numeric vector of sequence indices,
character vector (containing sequence name), or
logical vector (containing sequences to keep). If logical vector it
will be recycled as necessary to the same length as nrow.ms(x).
An MS object sampled from x as indicated by rows.
The bracket notation can return a set of sequences, or re-order rows.