多列上的R order（）方法给出错误“参数长度不同”

Question

实施例

c1 <- c(1,1,2,2)
c2 <- c(1,2,2,1)
c3 <- as.Date(c("2010-1-1", "2011-1-1", "2013-1-1", "2012-1-1"))

order(c3, decreasing = c(FALSE), method="radix")  # works
order(c1, c2, decreasing = c(TRUE, FALSE), method="radix")  # works
order(c1, c3, decreasing = c(TRUE, FALSE), method="radix")  # fails

为什么最后一个例子失败了？这是一个错误吗？