set.seed(456)
df<- data.frame( site= c(rep("Site1", 10), rep("Site2", 9)),genus= c(rep("sp1", 5), rep("sp2", 5), rep("sp1", 5),rep("sp2", 2),rep("sp3", 2) ), abun= rnorm(19, 10,1))

output<- data.frame( genus= c(rep("sp1", 5),rep("sp2", 5),rep("sp3",
2)), site1= c(9,22,74,86,79, 34,9,29,24,39,0,0), site2=c(38,22,76,83,
60, 66,85,0,0,0, 46,72))