r语言怎样取前n-1项均值？？

r语言怎样取前n-1项均值？？r语言怎样取前n-1项值？怎样做呢？

R语言获取指定列的均值（rowmeans & apply函数）_yqc_kayla_bbd的博客-CSDN博客_r语言求各列数据均值 R语言如何求取指定列的均值（rowMeans函数和apply函数）

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举例1到10，取前9项均值

> a <- (1:10)
> a
 [1]  1  2  3  4  5  6  7  8  9 10
> mean(a[1:(length(a)-1)])
[1] 5