R Arrays
Arrays
Compared to matrices, arrays can have more than two dimensions.
We can use the array() function to create an array, and the dim parameter to specify the dimensions:
Example
# An array with one dimension with values ranging from 1 to 24
thisarray <-
c(1:24)
thisarray
# An array with more than one dimension
multiarray <- array(thisarray, dim = c(4, 3, 2))
multiarray
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Example Explained
In the example above we create an array with the values 1 to 24.
How does dim=c(4,3,2) work?
The first and second number in the bracket specifies the amount of rows and columns.
The last number in the bracket specifies how many dimensions we want.
Note: Arrays can only have one data type.
Access Array Items
You can access the array elements by referring to the index position. You can use the [] brackets to
access the desired elements from an array:
Example
thisarray <- c(1:24)
multiarray <- array(thisarray, dim = c(4, 3, 2))
multiarray[2, 3, 2]
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The syntax is as follow: array[row position, column position, matrix level]
You can also access the whole row or column from a matrix in an array, by using the c() function:
Example
thisarray <- c(1:24)
# 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]
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A comma (,) before c() means that we want to access the column.
A comma (,) after c() means that we want to access the row.
Check if an Item Exists
To find out if a specified item is present in an array, use the %in% operator:
Example
Check if the value "2" is present in the array:
thisarray <- c(1:24)
multiarray <- array(thisarray, dim = c(4, 3, 2))
2 %in% multiarray
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Amount of Rows and Columns
Use the dim() function to find the amount of rows and columns in an array:
Example
thisarray <- c(1:24)
multiarray <- array(thisarray, dim = c(4, 3, 2))
dim(multiarray)
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Array Length
Use the length() function to find the dimension of an array:
Example
thisarray <- c(1:24)
multiarray <- array(thisarray, dim = c(4, 3, 2))
length(multiarray)
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Loop Through an Array
You can loop through the array items by using a for loop:
Example
thisarray <- c(1:24)
multiarray <- array(thisarray, dim = c(4, 3, 2))
for(x in multiarray){
print(x)
}
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