如何计算R（数据结构）中的平均值

我在R中有一个数据结构，如下所示：

> tkr[[i, 4]]
[1] 81.3
> tkr[[i - 1, 4]]
[1] 82.59
> tkr[[i - 2, 4]]
[1] 80.69
> tkr[[i - 3, 4]]
[1] 79.76
> tkr[[i - 4, 4]]
[1] 81.19
> tkr[[i - 5, 4]]
[1] 77.71
> tkr[[i - 6, 4]]
[1] 77.9
> tkr[[i - 7, 4]]
[1] 75.06
> tkr[[i - 8, 4]]
[1] 72.76
> tkr[[i - 9, 4]]
[1] 75.5

我想计算这10个值的平均值（行索引变化，列索引保持恒定在4）

我尝试了：mean（tkr[I:I-9，4]），得到了75.5，这只是最后一个数据点的值

平均值是78.446-这是我期望的值

有人能给我指一下正确的方向吗

dput(head(tkr))

structure(c(71, 71, 73, 71.35, 69.7, 70.43, 72.5, 73.3, 73.45, 
71.35, 72, 71.27, 70.2, 70.56, 70.89, 70, 69.18, 67.06, 71.44, 
73.08, 71.1, 70.41, 70.28, 67.56, 116744, 150669, 146162, 153921, 
145007, 356811), .indexCLASS = "Date", tclass = "Date", .indexTZ = "UTC", tzone = "UTC", src = "google", updated = structure(1415233768.37727, class = c("POSIXct", 
"POSIXt")), class = c("xts", "zoo"), index = structure(c(1380585600, 
1380672000, 1380758400, 1380844800, 1381104000, 1381190400), tzone = "UTC", tclass = "Date"), .Dim = c(6L, 
5L), .Dimnames = list(NULL, c("DATA.Open", "DATA.High", "DATA.Low", 
"DATA.Close", "DATA.Volume")))

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你没有放括号：

mean(tkr[i:(i - 9), 4])

或：

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您能把

dput（head（tkr））的结果添加到您的帖子中吗
mean(tkr[(i - 9):i, 4])