Vectorizing a matrix [duplicate]

Question

I have a large 2D matrix that is 1000 x 1000. I want to reshape this so that it is one column (or row). For example, if the matrix was:

A B C 1 4 7 2 5 8 3 6 9 

I want to turn it in to:

1 2 3 4 5 6 7 8 9

I do not need to preserve the column headers, just the order of the data. How do I do this using reshape2 (which is the package that I presumed was the easiest to use)?

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Just to clarify, I mentioned reshape as I thought it was the best way of doing this. I can see that there are simpler methods which I am perfectly happy with.

Answer 1

I think it will be difficult to find a more compact method than:

c(m) [1] 1 2 3 4 5 6 7 8 9 

However, if you want to retain a matrix structure, then this reworking of the dim attribute would be be effective:

dim(m) <- c(dim(m)[1]*dim(m)[2], 1) m       [,1]  [1,]    1  [2,]    2  [3,]    3  [4,]    4  [5,]    5  [6,]    6  [7,]    7  [8,]    8  [9,]    9 

There would be more compact methods of getting the product of the dimensions but the above method emphasizes that the dim attribute is a two element vector for matrices. Other ways of getting the "9" in that example include:

> prod(dim(m)) [1] 9 > length(m) [1] 9 

Answer 2

A possible solution, but without using reshape2:

> m <- matrix(c(1:9), ncol = 3) > m      [,1] [,2] [,3] [1,]    1    4    7 [2,]    2    5    8 [3,]    3    6    9 > as.vector(m) [1] 1 2 3 4 5 6 7 8 9