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R Arrays
Arrays
Compared to matrix, the same members can have more than two sizes.
We can use the array() function to create a list, and a dim parameter to specify a size:
Example
thisarray <- c(1:24)
thisarray
# An array with more than one dimension
multiarray <- array(thisarray, dim = c(4, 3, 2))
multiarray
Example Explained
In the example above we create a list of numbers 1 to 24.
How does dim = c (4,3,2) work?
The first and second numbers in parentheses determine the number of rows and columns.
The last number in parentheses indicates how many values we want.
Note: Lists can contain only one type of data.
Access Array Items
You can access the elements of the same members by referring to the index area. You can use [] brackets to access the desired elements in the list:
Example
multiarray <- array(thisarray, dim = c(4, 3, 2))
multiarray[2, 3, 2]
The syntax is as follows: list [row location, column location, matrix level]
You can also access the entire row or column from the matrix in the list, using the function c():
Example
# Access all the items from the first row from matrix one
multiarray <- array(thisarray, dim = c(4, 3, 2))
multiarray[c(1),,1]
# Access all the items from the first column from matrix one
multiarray <- array(thisarray, dim = c(4, 3, 2))
multiarray[,c(1),1]
The comma (,) before c () indicates that we want to reach the column.
The comma (,) after c () indicates that we want to reach the line.
Check if an Item Exists
To find out if something is listed, use %in% operator:
Example
Check if the value "2" is present in the array:
multiarray <- array(thisarray, dim = c(4, 3, 2))
2 %in% multiarray
Amount of Rows and Columns
Use the dim() function to find the number of rows and columns in an order:
Example
multiarray <- array(thisarray, dim = c(4, 3, 2))
dim(multiarray)
Array Length
Use the length() function to find the size of the same member:
Example
multiarray <- array(thisarray, dim = c(4, 3, 2))
length(multiarray)
Loop Through an Array
You can access the program properties via for loop:
Example
multiarray <- array(thisarray, dim = c(4, 3, 2))
for(x in multiarray){
print(x)
}