Arrays
In this lesson, we will learn what arrays are in R and how to create them.
We'll cover the following
Both data structures (vectors and lists) are one dimensional meaning they have only length and no other dimension.
On the plus side, arrays in R language can be n-dimensional. However, like vectors, arrays can store only values having the same data type.
Creating Arrays
In R, arrays can be created using the array() keyword. Inputs to array() include concatenated vectors and the dim argument for creating an array.
Syntax for Creating Arrays
array(<dataVectors>, dim = <vectorOfDimensions>)
Optionally, we can also provide names for each dimension!
Let’s begin with making a simple two-dimensional array with one vector.
myVector <- c (1, 2, 3) # create a vectormyArray <- array (myVector, dim = c(3, 1))print (myArray)
The dimensions of this array are where the number of rows is and the number of columns is . This is also called a single column matrix.
Notice the row and column labels that are displayed on the console by using print() with an array.
The illustration above shows the meaning of the row and column labels displayed when an array is printed.
Now let’s code an array that has only one row but multiple columns:
myVector <- c (1, 2, 3) # create a vectormyArray <- array (myVector, dim = c(1,3))print (myArray)
The dimensions of this array are where the number of rows is and the number of columns is . This is also called a single row matrix.
Now let’s create an array of dimensions :
myVector <- c (1, 2, 3, 4) # create a vectormyArray <- array (myVector, dim = c(2, 2))print(myArray)
Now let’s see how to create an array of two matrices each with rows and columns.
myVector1 <- c (1, 2, 3)myVector2 <- c (4, 5, 6)myVector3 <- c (7, 8, 9)myArray <- array (c(myVector1, myVector2, myVector3), dim = c(3, 3, 2))print (myArray)
Here, in line number 5
dim = c(3, 3, 2)
# First argument is the number of rows, the second argument is the number of columns and the third argument is the number of matrices.
There are two matrices (notice the last argument) of size .
Now, let’s try making an array using vectors of different sizes.
myVector1 <- c (1, 2, 3)myVector2 <- c (4, 5, 6, 7, 8, 9)myArray <- array (c(myVector1, myVector2), dim = c(3, 3, 2))print (myArray)
Accessing and Modifying Arrays
We can access a specific element of the array using the square brackets []. Below is an example code to demonstrate how to access arrays.
myVector1 <- c (1, 2, 3)myVector2 <- c (4, 5, 6, 7, 8, 9)myArray <- array (c(myVector1, myVector2), dim = c(3, 3, 2))# Accessing the element located at row 1, column 1 in the first matrixprint (myArray[1, 1, 1])# Accessing the element located at row 2, column 3 in the second matrixprint (myArray[2, 3, 2])
We can access an element based on a single index as well. R language uses column major order which means if only a single index is used to access an array, then the first indexes will belong to the first rows of the first column.
Let’s have a look at an illustration:
Let’s have a look at the code:
In the illustration above "e" has index , and our code prints "e" when index is accessed.
myVector <- c ("a", "b", "c", "d", "e", "f", "g", "h", "i")myArray <- array (myVector, dim = c(3, 3, 1))print(myArray[5]) # Uses column major for accessing this index
We can also modify an element in an array using the two methods:
myVector <- c ("a", "b", "c", "d", "e", "f", "g", "h", "i")myArray <- array (myVector, dim = c(3, 3, 2))print("Original Array:")print(myArray)myArray[2, 2, 2] = "E" # Modifying the element located at row 2, column 2 in the second matrixprint("Modified Array:")print (myArray)