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Nov 4, 2019 in R Language

Q:

R Matrix Tutorial: Create, Print, add Column, Slice

1 Answer

Nov 4, 2019

A matrix is a 2-dimensional array that has m number of rows and n number of columns. In other words, matrix is a combination of two or more vectors with the same data type.

Note: It is possible to create more than two dimensions arrays with R.

We can create a matrix with the function matrix(). This function takes three arguments:

matrix(data, nrow, ncol, byrow = FALSE)

Arguments: 

  • data: The collection of elements that R will arrange into the rows and columns of the matrix \
  • nrow: Number of rows 
  • ncol: Number of columns 
  • byrow: The rows are filled from the left to the right. We use `byrow = FALSE` (default values), if we want the matrix to be filled by the columns i.e. the values are filled top to bottom.

Let's construct two 5x2 matrix with a sequence of number from 1 to 10, one with byrow = TRUE and one with byrow = FALSE to see the difference.

You can add a column to a matrix with the cbind() command. cbind() means column binding. cbind()can concatenate as many matrix or columns as specified. For example, our previous example created a 5x2 matrix. We concatenate a third column and verify the dimension is 5x3

Example:

# concatenate c(1:5) to the matrix_a
matrix_a1 <- cbind(matrix_a, c(1:5))
# Check the dimension
dim(matrix_a1)

Output:

## [1] 5 3We can select elements one or many elements from a matrix by using the square brackets [ ]. This is where slicing comes into the picture.

For example:

  • matrix_c[1,2] selects the element at the first row and second column.
  • matrix_c[1:3,2:3] results in a matrix with the data on the rows 1, 2, 3 and columns 2, 3,
  • matrix_c[,1] selects all elements of the first column.
  • matrix_c[1,] selects all elements of the first row.
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