错误dim(X)必须有一个正长度?

I want to compute the mean of "Population" of built-in matrix state.x77. The codes are :

我想计算内建矩阵的“总体”的均值。代码是:

apply(state.x77[,"Population"],2,FUN=mean)

#Error in apply(state.x77[, "Population"], 2, FUN = mean) : 

# dim(X) must have a positive length

how can I prevent this error? If I use $ sign

我怎样才能避免这个错误呢?如果我使用$符号。

apply(state.x77$Population,2,mean)
# Error in state.x77$Population : $ operator is invalid for atomic vectors

What is atomic vector?

原子的矢量是什么?

1 个解决方案

#1

To expand on joran's comments, consider:

若要扩展joran的评论，请考虑:

> is.vector(state.x77[,"Population"])
[1] TRUE
> is.matrix(state.x77[,"Population"])
[1] FALSE

So, your Population data is now no diferent from any other vector, like 1:10, which has neither columns or rows to apply against. It is just a series of numbers with no more advanced structure or dimension. E.g.

所以，你的人口数据现在和其他任何向量都没有区别，比如1:10，它既没有列也没有行来反对。它只是一系列没有更高级的结构或维度的数字。如。

> apply(1:10,2,mean)
Error in apply(1:10, 2, mean) : dim(X) must have a positive length

Which means you can just use the mean function directly against the matrix subset which you have selected: E.g.:

也就是说，你可以直接用平均函数来对抗你选择的矩阵子集:例如:

> mean(1:10)
[1] 5.5
> mean(state.x77[,"Population"])
[1] 4246.42

To explain 'atomic' vector more, see the R FAQ again (and this gets a bit complex, so hold on to your hat)...

为了更详细地解释“原子”矢量，请再次查看R FAQ(这有点复杂，所以请坚持你的帽子)……

R has six basic (‘atomic’) vector types: logical, integer, real, complex, string (or character) and raw. http://cran.r-project.org/doc/manuals/r-release/R-lang.html#Vector-objects

R有六个基本的(“原子”)向量类型:逻辑、整数、实数、复杂、字符串(或字符)和raw。http://cran.r-project.org/doc/manuals/r-release/R-lang.html矢量对象

So atomic in this instance is referring to vectors as the basic building blocks of R objects (like atoms make up everything in the real world).

在这个例子中，原子是指向量作为R对象的基本构件(就像原子构成了现实世界中的一切)。

If you read R's inline help by entering ?"$" as a command, you will find it says:

如果你通过输入“$”来读取R的内联帮助，你会发现它说:

‘$’ is only valid for recursive objects, and is only discussed in the section below on recursive objects.

“$”只对递归对象有效，并且只在递归对象上的节中讨论。

Since vectors (like 1:10) are basic building blocks ("atomic"), with no recursive sub-elements, trying to use $ to access parts of them will not work.

由于向量(如1:10)是基本的构建块(“原子”)，没有递归子元素，因此试图使用$来访问它们的部分将不起作用。

Since your matrix (statex.77) is essentially just a vector with some dimensions, like:

因为你的矩阵(statex.77)本质上就是一个具有某些维度的向量，比如:

> str(matrix(1:10,nrow=2))
 int [1:2, 1:5] 1 2 3 4 5 6 7 8 9 10

...you also can't use $ to access sub-parts.

…您也不能使用$访问子部分。

> state.x77$Population
Error in state.x77$Population : $ operator is invalid for atomic vectors

But you can access subparts using [ and names like so:

但是您可以使用[和这样的名称访问子部件:

> state.x77[,"Population"]
   Alabama         Alaska        Arizona...
      3615            365           2212...

#1