将矩阵转换为列表 [英] converting a matrix to a list

问题描述

假设我有一个矩阵foo，如下所示:

Suppose I have a matrix foo as follows:

foo <- cbind(c(1,2,3), c(15,16,17))

> foo
     [,1] [,2]
[1,]    1   15
[2,]    2   16
[3,]    3   17

我想将其变成一个看起来像

I'd like to turn it into a list that looks like

[[1]]
[1]  1 15

[[2]]
[1]  2 16

[[3]]
[1]  3 17

您可以按照以下步骤进行操作:

You can do it as follows:

lapply(apply(foo, 1, function(x) list(c(x[1], x[2]))), function(y) unlist(y))

我对没有那么复杂的替代方法感兴趣.请注意，如果您只是执行apply(foo, 1, function(x) list(c(x[1], x[2])))，它将返回列表中的一个列表，我希望避免这种情况.

I'm interested in an alternative method that isn't as complicated. Note, if you just do apply(foo, 1, function(x) list(c(x[1], x[2]))), it returns a list within a list, which I'm hoping to avoid.

推荐答案

这是一个更干净的解决方案:

Here's a cleaner solution:

as.list(data.frame(t(foo)))

这利用了一个事实，即数据帧实际上只是等长向量的列表(而矩阵实际上是一个显示有列和行的向量...您可以通过调用foo [5]来看到这一点) (例如).

That takes advantage of the fact that a data frame is really just a list of equal length vectors (while a matrix is really a vector that is displayed with columns and rows...you can see this by calling foo[5], for instance).

您也可以这样做，尽管并没有太大改善:

You could also do this, although it isn't much of an improvement:

lapply(1:nrow(foo), function(i) foo[i,])

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