Matrices can be constructed in RStudio using the matrix command:
matrix( data, nrow, ncol, byrow )
The input arguments for this command are:
| Argument | Description |
|---|---|
| data | A vector containing all of the values to be entered into the matrix. |
| nrow | The number of rows that the matrix should have. |
| ncol | The number of columns that the matrix should have. |
| byrow | A logical argument denoting whether the contents of data should be inserted by row (TRUE) or by column (FALSE - default) |
As an illustration, lets create the three matrices below.
A <- matrix( 1:9, nrow=3, ncol=3, byrow=FALSE )
B <- matrix( c(1, 9, -13, 20, 5, -6), nrow=2, ncol=3, byrow=TRUE )
C <- matrix( rep(2,6), nrow=3, ncol=2, byrow=FALSE )
Note that the length of the data vector must be equivalent to the number of elements in the matrix, i.e. for a nrowncol matrix, the length of the data vector must be nrow*ncol. If this is not the case, then RStudio would will cycle through the data vector until a value has been entered into each element of the matrix. Furthermore, if the number of matrix elements is not a multiple of the data vector’s length, then a warning message is produced in the console. Try the following example to understand how the data is entered into matrices
a <- 1:5
matrix(a, ncol=5, nrow=2, byrow=FALSE)
matrix(a, ncol=2, nrow=2, byrow=FALSE)
matrix(a, ncol=3, nrow=4, byrow=FALSE)