聚类抽样中的问题：'mixed with negative subscripts'

Question

我试图进行集群采样，但遇到了以下错误：Error in xj[i] : only 0's may be mixed with negative subscripts原因是什么？如何避开？谢谢你的帮助！

这是代码：

#simulate some data
y <- rnorm(20)
x <- rnorm(20)
z <- rep(1:5, 4)
w <- rep(1:4, each=5)
dd <- data.frame(id=z, cluster=w, x=x, y=y)
clusters <- split(dd, dd$cluster) #split into clusters
k <- length(clusters) #length of clusters
# This function generates a cluster sample
clsamp <- function() dd[unlist(clusters[sample.int(k, k, replace = TRUE)], use.names = TRUE), ]
clsamp()

我得到了这个错误：Error in xj[i] : only 0's may be mixed with negative subscripts

Answer 1

找到答案：将分割线更改为clusters <- split(seq_len(nrow(dd)), dd$cluster)