A list with three components:
First, a data frame with rows corresponding to all individuals (across the
two sets of individual IDs) and three columns: indexInFirst and
indexInSecond contain numeric indices to the locations of the
individuals within cross and pheno, and inBoth is a
logical vector to indicate which individuals appear in both crosses. The
row names are the individual identifiers.
The second and third components are vectors of indices in id1 and
id2, respectively, indicating the paired locations of the individuals
that are in common.