read_symbol_map() reads MRK_List1.rpt data and returns an efficient
data table to be used for marker symbol remapping.
This function is memoised.
read_symbol_map(report_file = NULL, n_max = Inf)A data.table where each row is a mapping,
from marker_symbol to marker_symbol_now:
marker_symbol (set as key): marker symbol is a unique abbreviation of the marker name.
marker_symbol_now: genetic marker symbol replacement. If the record pertains a marker_symbol that was withdrawn, then marker_symbol_now indicates the most recent in-use marker symbol that replaced it.
The path to a MRK_List1.rpt file. Leave this as NULL
and the function will automatically download the report from
https://www.informatics.jax.org/downloads/reports/MRK_List1.rpt.
Maximum number of lines to read.