combinations

combinations.r

n <- 5
a <- combn(c(1:(2*n)), 2)
b <- combn(1:ncol(a), n)
l <- list()
m <- list()
j <- 1
for(i in 1:ncol(b))
{
	x <- a[, b[,i]]
	if(!any(duplicated(c(x))))
	{
		l[[j]] <- x
		m[[j]] <- b[,i]
		j <- j + 1
	}
}



library(gtools)
library(dplyr)
fun <- function(n)
{
	p <- permutations(n, n, 1:n)
	o <- lapply(1:nrow(p), function(x)
	{
		x <- matrix(p[x,], nrow=2)
		x <- apply(x, 2, sort)
		x <- x[,order(x[1,])]
		return(x)
	}) %>% unique
	o <- unique(o)
	return(o)
}

fun(4)
fun(10)