使用向量的r子集数组 [英] r subset array using vector

问题描述

我觉得这个问题应该已经回答了，但是我没有找到.我有一个数组，我想使用向量将其子集化.我知道很难做到这一点，但是我敢肯定必须有一种简单的方法.有什么想法吗?

I feel like this question should have already been answered, but I found none. I have an array and I want to subset it using a vector. I know how to do it the hard way, but I'm sure there's got to be an easy way. Any ideas?

这是我的例子:

dat <- data.frame(a = rep(letters[1:3], 2), b = rep(letters[1:2], 3), c = c(rep("a", 5), "b"), x = rnorm(6), stringsAsFactors = FALSE)

l <- by(dat[ , "x"], dat[ , 1:3], mean)

l["a", "a", "a"] # works  
l[c("a", "a", "a")] # does not work

所以我想我需要一种方法来将c()包装器形式c("a", "a", "a")传递给l.

So I guess I need to a way to remove the c() wrapper form c("a", "a", "a") before passing it to l.

推荐答案

可以使用矩阵代替向量:

Instead of a vector you could use a matrix:

l[matrix(rep("a", 3), nrow=1)]

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