Access Specific Elements, Rows, and Columns in an R Matrix

R Programming: Matrix Exercise-4 with Solution

Write a R program to access the element at 3^rd column and 2^nd row, only the 3^rd row and only the 4^th column of a given matrix.

Sample Solution:

R Programming Code:

# Define row names for the matrix
row_names = c("row1", "row2", "row3", "row4")

# Define column names for the matrix
col_names = c("col1", "col2", "col3", "col4")

# Create a matrix with values from 1 to 16, specifying number of rows, filling by row, and naming rows and columns
M = matrix(c(1:16), nrow = 4, byrow = TRUE, dimnames = list(row_names, col_names))

# Print a message indicating that the following output is the original matrix
print("Original Matrix:")

# Print the matrix to the console
print(M)

# Print a message indicating that the following output is the element at 3rd column and 2nd row
print("Access the element at 3rd column and 2nd row:")

# Access and print the element located at the 2nd row and 3rd column of the matrix
print(M[2,3])

# Print a message indicating that the following output is the 3rd row of the matrix
print("Access only the 3rd row:")

# Access and print only the 3rd row of the matrix
print(M[3,])

# Print a message indicating that the following output is the 4th column of the matrix
print("Access only the 4th column:")

# Access and print only the 4th column of the matrix
print(M[,4])

Output:

[1] "Original Matrix:"
     col1 col2 col3 col4
row1    1    2    3    4
row2    5    6    7    8
row3    9   10   11   12
row4   13   14   15   16
[1] "Access the element at 3rd column and 2nd row:"
[1] 7
[1] "Access only the  3rd row:"
col1 col2 col3 col4 
   9   10   11   12 
[1] "Access only the 4th column:"
row1 row2 row3 row4 
   4    8   12   16                 

Explanation:

• Define Row Names:
• row_names = c("row1", "row2", "row3", "row4")
• Creates a vector with names for the rows of the matrix.
• Define Column Names:
• col_names = c("col1", "col2", "col3", "col4")
• Creates a vector with names for the columns of the matrix.
• Create Matrix:
• M = matrix(c(1:16), nrow = 4, byrow = TRUE, dimnames = list(row_names, col_names))
• Creates a 4x4 matrix filled with numbers from 1 to 16.
• nrow = 4: Specifies that the matrix should have 4 rows.
• byrow = TRUE: Fills the matrix by rows (row-major order).
• dimnames = list(row_names, col_names): Assigns row and column names to the matrix.
• Print Original Matrix:
• print("Original Matrix:")
• Prints a message indicating that the next output is the original matrix.
• print(M)
• Prints the contents of the matrix M.
• Access Element at Specific Position:
• print("Access the element at 3rd column and 2nd row:")
• Prints a message indicating that the next output is the element at the 2nd row and 3rd column.
• print(M[2,3])
• Accesses and prints the element located at the 2nd row and 3rd column of the matrix.
• Access Specific Row:
• print("Access only the 3rd row:")
• Prints a message indicating that the next output is the 3rd row of the matrix.
• print(M[3,])
• Accesses and prints all elements of the 3rd row of the matrix.
• Access Specific Column:
• print("Access only the 4th column:")
• Prints a message indicating that the next output is the 4th column of the matrix.
• print(M[,4])
• Accesses and prints all elements of the 4th column of the matrix.

R Programming Code Editor:

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