Question: “How can I access a single column or row from a matrix?”

If you have a matrix, how do you access a specific column or row in it?

Data

We’ll use a small set of data that I will make below. I will one vectors comprised numbers from 1 to 9.

X <- c(1,2,3,4,5,6,7,8,9)

Next, let’s create a matrix and put our vector in it to create a 3x3 matrix.

example_matrix <- matrix(X,
                  byrow = T,
                  nrow = 3)

example_matrix
##      [,1] [,2] [,3]
## [1,]    1    2    3
## [2,]    4    5    6
## [3,]    7    8    9

To access a specific full column or full row, we use brackets. Bracket notation is used to refer to row first, then column: [row #, column#]

#to access the entirety of one column
example_matrix[,1]
## [1] 1 4 7
#to access the entirety of one row
example_matrix[1,]
## [1] 1 2 3