我用R做了Kmeans聚类，可是想输出结果时提示错误于as.data.frame.default(x[[i]], optional = TRUE, stringsAsFactors = stringsAsFactors) :   cannot coerce class '"kmeans"' into a data.frame

全部语句如下：
> x<-read.csv("sl.csv")
> y<-scale(x)
> k3<-kmeans(y,3)
> plotcluster(y,k3$cluster)
> write.csv(k3,"kjl.csv")
错误于as.data.frame.default(x[[i]], optional = TRUE, stringsAsFactors = stringsAsFactors) :
  cannot coerce class '"kmeans"' into a data.frame
>

哪位大侠帮忙看看，坐等高手回复，谢谢