从 n x m 矩阵转换为 R 中的长矩阵 [英] Convert from n x m matrix to long matrix in R

问题描述

注意:这不是图形问题.

Note: This is not a graph question.

我有一个 n x m 矩阵:

I have an n x m matrix:

> m = matrix(1:6,2,3)
> m
  a  b  c
d 1  2  3
e 4  5  6

我想将其转换为长矩阵:

I would like to convert this to a long matrix:

> m.l
a d 1
a e 4
b d 2
b e 5
c d 3
c e 6

显然嵌套 for 循环可以工作，但我知道有很多很好的工具可以在 R 中重塑矩阵.到目前为止，我只找到了关于从长矩阵或宽矩阵转换为 nxm 矩阵的文献，而不是相反的方法.我错过了一些明显的东西吗?我该如何进行这种转换?

Obviously nested for loops would work but I know there are a lot of nice tools for reshaping matrixes in R. So far, I have only found literature on converting from long or wide matrixes to an n x m matrix and not the other way around. Am I missing something obvious? How can I do this conversion?

谢谢！

推荐答案

如果你需要单列矩阵

 matrix(m, dimnames=list(t(outer(colnames(m), rownames(m), FUN=paste)), NULL))
 #    [,1]
 #a d    1
 #a e    4
 #b d    2
 #b e    5
 #c d    3
 #c e    6

对于 data.frame 输出，您可以使用 reshape2

For a data.frame output, you can use melt from reshape2

 library(reshape2)
 melt(m)

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