R Matrices
Matrices
A matrix is a two dimensional data set with columns and rows.
A column is a vertical representation of data, while a row is a horizontal representation of data.
A matrix can be created with the matrix() function. Specify the nrow and ncol parameters to get the amount of rows and columns:
Example
# Create a matrix
thismatrix <- matrix(c(1,2,3,4,5,6), nrow = 3, ncol = 2)
# Print the matrix
thismatrix
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Note: Remember the c() function is used to concatenate items together.
You can also create a matrix with strings:
Example
thismatrix <- matrix(c("apple", "banana", "cherry", "orange"), nrow = 2, ncol = 2)
thismatrix
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Access Matrix Items
You can access the items by using [ ] brackets. The first number "1" in the bracket specifies the row-position, while the second number "2" specifies the column-position:
Example
thismatrix <- matrix(c("apple", "banana", "cherry", "orange"), nrow = 2, ncol = 2)
thismatrix[1, 2]
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The whole row can be accessed if you specify a comma after the number in the bracket:
Example
thismatrix <- matrix(c("apple", "banana", "cherry", "orange"), nrow = 2, ncol = 2)
thismatrix[2,]
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The whole column can be accessed if you specify a comma before the number in the bracket:
Example
thismatrix <- matrix(c("apple", "banana", "cherry", "orange"), nrow = 2, ncol = 2)
thismatrix[,2]
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Access More Than One Row
More than one row can be accessed if you use the c() function:
Example
thismatrix <- matrix(c("apple", "banana", "cherry", "orange","grape", "pineapple", "pear", "melon", "fig"), nrow = 3, ncol = 3)
thismatrix[c(1,2),]
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Access More Than One Column
More than one column can be accessed if you use the c() function:
Example
thismatrix <- matrix(c("apple", "banana", "cherry", "orange","grape", "pineapple", "pear", "melon", "fig"), nrow = 3, ncol = 3)
thismatrix[, c(1,2)]
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Add Rows and Columns
Use the cbind() function to add additional columns in a Matrix:
Example
thismatrix <- matrix(c("apple", "banana", "cherry", "orange","grape", "pineapple", "pear", "melon", "fig"), nrow = 3, ncol = 3)
newmatrix <- cbind(thismatrix, c("strawberry", "blueberry", "raspberry"))
# Print the new matrix
newmatrix
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Note: The cells in the new column must be of the same length as the existing matrix.
Use the rbind() function to add additional rows in a Matrix:
Example
thismatrix <- matrix(c("apple", "banana", "cherry", "orange","grape", "pineapple", "pear", "melon", "fig"), nrow = 3, ncol = 3)
newmatrix <- rbind(thismatrix, c("strawberry", "blueberry", "raspberry"))
# Print the new matrix
newmatrix
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Note: The cells in the new row must be of the same length as the existing matrix.
Remove Rows and Columns
Use the c() function to remove rows and columns in a Matrix:
Example
thismatrix <- matrix(c("apple", "banana", "cherry", "orange", "mango", "pineapple"), nrow = 3, ncol =2)
#Remove the first row and the first column
thismatrix <- thismatrix[-c(1), -c(1)]
thismatrix
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Check if an Item Exists
To find out if a specified item is present in a matrix, use the %in% operator:
Example
Check if "apple" is present in the matrix:
thismatrix <- matrix(c("apple", "banana", "cherry", "orange"), nrow = 2, ncol = 2)
"apple" %in% thismatrix
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Number of Rows and Columns
Use the dim() function to find the number of rows and columns in a Matrix:
Example
thismatrix <- matrix(c("apple", "banana", "cherry", "orange"), nrow = 2, ncol = 2)
dim(thismatrix)
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Matrix Length
Use the length() function to find the dimension of a Matrix:
Example
thismatrix <- matrix(c("apple", "banana", "cherry", "orange"), nrow = 2, ncol = 2)
length(thismatrix)
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Total cells in the matrix is the number of rows multiplied by number of columns.
In the example above: Dimension = 2*2 = 4.
Loop Through a Matrix
You can loop through a Matrix using a for loop. The loop will start at the first row, moving right:
Example
Loop through the matrix items and print them:
thismatrix <- matrix(c("apple", "banana", "cherry", "orange"), nrow = 2, ncol = 2)
for (rows in 1:nrow(thismatrix)) {
for (columns in 1:ncol(thismatrix)) {
print(thismatrix[rows, columns])
}
}
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Combine two Matrices
Again, you can use the rbind() or cbind() function to combine two or more matrices together:
Example
# Combine matrices
Matrix1 <- matrix(c("apple", "banana", "cherry", "grape"), nrow = 2, ncol = 2)
Matrix2 <- matrix(c("orange", "mango", "pineapple", "watermelon"), nrow = 2, ncol = 2)
# Adding it as a rows
Matrix_Combined <- rbind(Matrix1, Matrix2)
Matrix_Combined
# Adding it as a columns
Matrix_Combined <- cbind(Matrix1, Matrix2)
Matrix_Combined
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