Exclude rows where element has been previously met for N times - r

Question

I have following input data:
# [,1] [,2]
#[1,] "A" "B"
#[2,] "A" "C"
#[3,] "A" "D"
#[4,] "B" "C"
#[5,] "B" "D"
#[6,] "C" "D"
Next I want to exclude rows where first or second element has been previously for N times. For example if N = 2 then need to exclude following rows:
#[3,] "A" "D" - element "A" has been 2 times
#[5,] "B" "D" - element "B" has been 2 times
#[6,] "C" "D" - element "C" has been 2 times
Note: Need to take into account excluding results immediately. For example if element has met 5 times and after removing it met only 1 times then need to leave next row with this element. Because now it meets 2 times.
Example (N=2):
Input data:
[,1] [,2]
[1,] "A" "B"
[2,] "A" "C"
[3,] "A" "D"
[4,] "A" "E"
[5,] "B" "C"
[6,] "B" "D"
[7,] "B" "E"
[8,] "C" "D"
[9,] "C" "E"
[10,] "D" "E"
Output data:
[,1] [,2]
[1,] "A" "B"
[2,] "A" "C"
[5,] "B" "C"
[10,] "D" "E"

Answer 1

There are possibly more elegant solutions... but this seems to work:
v <- c("A", "B", "C", "D", "E")
cmb <- t(combn(v, 2))
n <- 2
# Go through each letter
for (l in v)
{
# Find the combinations using that letter
rows <- apply(cmb, 1, function(x){l %in% x})
rows.2 <- which(rows==T)
if (length(rows.2)>n)
rows.2 <- rows.2[1:n]
# Take the first n rows containing the letter,
# then append all the ones not containing it
cmb <- rbind(cmb[rows.2,], cmb[rows==F,])
}
cmb
which outputs:
[,1] [,2]
[1,] "D" "E"
[2,] "B" "C"
[3,] "A" "C"
[4,] "A" "B"