Create 2 dim List from 2 Dim list

Question

I have a 2 dim List where I need to create a new 2 dim List but only using certain elements form the original one:

The original list looks like this:

a = [['Volvo',100,200,300],['SAAB',10,20,30],['Ford',7,8,9]]

and I need to create a new 2 dimensional list that picks element 1 and 4 from the original list:

[['Volvo',300],['SAAB',30],['Ford',9]]

This is how I started building the solution but I don't understand how to create the new List? I don't think I can use append?

num_cols = len(a[0])
num_rows = len(a)
for i in range(num_rows)
  elem_1 = a[i][0]
  elem_2 = a[i][num_cols-1]

Or maybe something like this:

arr_2d=[]
for x in range(num_rows):
   column_elements = []
   for y in range(num_cols):
       # Enter the all the values w.r.t to a particular column
       column_elements.append(a[x][0])
       column_elements.append(a[x][num_cols-1])
   #Append the column to the array.
   arr_2d.append(column_elements)
print(arr_2d)

Answer 1

This solved my problem. many thanks for the help!

num_cols = len(a[0])
arr_2d=[]
for x in range(number_of_rows):
   
    column_elements = []
    column_elements.append(a[x][0])
    column_elements.append(int(a[x][num_cols - 1]))

    arr_2d.append(column_elements)

print(arr_2d)

Answer 2

This is your answer:

a = [['Volvo', 100, 200, 300], ['SAAB', 10, 20, 30], ['Ford', 7, 8, 9]]
final_list = []

for i in range(len(a)):
    b = [a[i][0], a[i][-1]]
    final_list.append(b)

print(final_list)

and it will print this:

[['Volvo', 300], ['SAAB', 30], ['Ford', 9]]

note:

• There is no : at the end of for loop
• Didn't add new variable to the list

Answer 3

You want a new list. In which case a trivial list comprehension will help you - ie, no explicit loop constructs required:

a = [['Volvo',100,200,300],['SAAB',10,20,30],['Ford',7,8,9]]

b = [[e[0], e[-1]] for e in a]

print(b)

Output:

[['Volvo', 300], ['SAAB', 30], ['Ford', 9]]