#データフレーム内のデータの重複を探し出す関数
check.dup <- function(df){
	res <- setdiff(rownames(df), rownames(unique(df)))
	df[res,]
}

# 使用方法
test <- as.data.frame(matrix(c("a","a","b","b","c","c","1","2","2","2","2","3"), ncol=2))
check.dup(test)