Question

For this lab, you will work with two-dimensional lists in Python. Do the following:

1. Write a function that returns the sum of all the elements in a specified column in a matrix using the following header:

   def sumColumn(matrix, columnIndex)

2. Write a function display() that displays the elements in a matrix row by row, where the values in each row are displayed on a separate line. Use a single space to separate different values. Sample output from this function when it is called on a 3 X 4 matrix is as follows:

   2.5 3.0 4.0 1.5
   1.5 4.0 2.0 7.5
   3.5 1.0 1.0 2.5
   

3. Given this partial code

   def getMatrix(numRows, numColumns):
       '''returns a matrix with the specified number of rows and columns'''
       m = [] # the 2D list (i.e., matrix), initially empty
       for row in range(numRows):
           matrix_dimensions_string = str(numRows) + "-by-" + str(numColumns)
           line = input("Enter a " + matrix_dimensions_string + " matrix row for row " + str(row) + ": ")
       
           
       return m    

   write a function called getMatrix(numRows, numColumns) that returns a matrix with numRows rows and numColumns columns. The function reads the values of the matrix from the user on a row by row basis. The values of each row must be entered on one line using a space to separate the values. Use loops in your solution. A sample run of this function when it is caled as getMatrix(3, 4) to return a 3 by 4 matrix is as follows. Values shown in red are entered by the user:

   Enter a 3-by-4 matrix row for row 0: 2.5 3 4 1.5
   Enter a 3-by-4 matrix row for row 1: 1.5 4 2 7.5
   Enter a 3-by-4 matrix row for row 2: 3.5 1 1 2.5
   

Use the following function to test your code:

def main():
    m = getMatrix(3, 4)
    print("\nThe matrix is")
    display(m)

    print()
    for col in range(len(m[0])):
        print("Sum of elements for column %d is %.2f" % (col, sumColumn(m,col)))          

main()

A sample program run is as follows:

Enter a 3-by-4 matrix row for row 0: 1 22 3.7869 8
Enter a 3-by-4 matrix row for row 1: 4 5.6543 3 3
Enter a 3-by-4 matrix row for row 2: 1 1 1 1

The matrix is
1.0 22.0 3.7869 8.0 
4.0 5.6543 3.0 3.0 
1.0 1.0 1.0 1.0 

Sum of elements for column 0 is 6.00
Sum of elements for column 1 is 28.65
Sum of elements for column 2 is 7.79
Sum of elements for column 3 is 12.00

The format of the input and output of your program must be as in the sample run.

Answer 1

Program

def getMatrix(numRows, numColumns):
    '''returns a matrix with the specified number of rows and columns'''
    m = [] # the 2D list (i.e., matrix), initially empty
    for row in range(numRows):
        matrix_dimensions_string = str(numRows) + "-by-" + str(numColumns)
        line = input("Enter a " + matrix_dimensions_string + " matrix row for row " + str(row) + ": ")
        row = line.split(' ')
        row = [float(i) for i in row]
        m.append(row)
      
      
    return m

def display(m):
    for row in m:
        print (" ".join([str(col) for col in row]))
      
def sumColumn(matrix, columnIndex):
    return sum([row[columnIndex] for row in matrix])

def main():
    m = getMatrix(3,4)
    print("\nThe matrix is")
    display(m)

    print()
    for col in range(len(m[0])):
        print("Sum of elements for column %d is %.2f" % (col, sumColumn(m,col)))        

main()

Output

Enter a 3-by-4 matrix row for row 0: 1 22 3.7869 8
Enter a 3-by-4 matrix row for row 1: 4 5.6543 3 3
Enter a 3-by-4 matrix row for row 2: 1 1 1 1

The matrix is
1.0 22.0 3.7869 8.0
4.0 5.6543 3.0 3.0
1.0 1.0 1.0 1.0

Sum of elements for column 0 is 6.00
Sum of elements for column 1 is 28.65
Sum of elements for column 2 is 7.79
Sum of elements for column 3 is 12.00

Screenshot