To count how many elements of two sets overlap, one could write a custom function:
xtab_set <- function(A, B){
both <- union(A, B)
inA <- both %in% A
inB <- both %in% B
return(table(inA, inB))
}
A = 1:20
B = 10:30
xtab_set(A, B)
# inB
# inA FALSE TRUE
# FALSE 0 10
# TRUE 9 11
A Venn diagram, offered by various packages, can be used to visualize overlap counts across multiple sets.