A matrix is a vector represented and accessible in two dimensions. Therefore, what applies to vectors is most likely to apply to a matrix. For example, each type of vector (for example, numeric vector or logical vectors) has its matrix version, that is, there are numeric matrices, logical matrices, and so on.
We can call matrix() to create a matrix from a vector by setting up one of its two dimensions:
matrix(c(1, 2, 3, 2, 3, 4, 3, 4, 5), ncol = 3) ## [,1] [,2] [,3] ## [1,] 1 2 3 ## [2,] 2 3 4 ## [3,] 3 4 5
By specifying ncol = 3, we mean that the provided vector should be regarded as a matrix with 3 columns (and 3 rows automatically). You may feel the original vector is not as straightforward as its representation. To make the code more user-friendly, we can write the vector in multiple lines:
matrix(c(1, 2, 3, 4, 5, 6, 7, 8, 9), nrow = 3, byrow = FALSE) ## [,1] [,2] [,3] ## [1,] 1 4 7 ## [2,] 2 5 8 ## [3,] ...