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Python

Shane Singh
Shane Singh
5,440 Points
Posted by Shane Singh
Shane Singh
5,440 Points

Transposing my array?

I am a novice programmer in python and was wondering if I can get a little help. The code I am about to show below prints out a simple array based on the users input for # of rows and # of columns. 

new_list = []

undersc = '_'

for i in range(1, rows + 1):

      new = []

      for j in range(1, columns + 1)     

        new.append(undersc if j > i else 'Z')

      new_list.append(new)

for c in range(len(new_list[0])): 

     print()

for r in range(len(new_list)):

     for c in range(len(new_list[0]))       

       array = print((new_list[r][c]), end=" ")   

     print()

return array

The console outputs the following:

Z _  _  _  _

Z  Z  _  _  _

Z  Z  Z   _  _

I am completely lost as to how I would transpose my array in other words swap the columns with the rows. Any help would be greatly appreciated!

1 Answer

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,423 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,423 Points

You have all the information you need. To reverse the columns and rows exchange your inner and outer loops:

# initial print loop
    for r in range(len(new_list)):
        for c in range(len(new_list[0])):
            array = print((new_list[r][c]), end=" ")
        print()


# transposed print loops
    for c in range(columns):
        for r in range(rows):
            array = print((new_list[r][c]), end=" ")
        print()

Compressing and cleaning up your code a bit:

def array2(rows, columns):
    new_list = []
    undersc = '_'

    # i and j are relative counters, no need to use 1-based counting
    for i in range(rows):
        new = []
        for j in range(columns):
            new.append(undersc if j > i else 'Z')
        new_list.append(new)

    # this prints out many blank lines. Not clear why it's needed
    # for c in range(len(new_list[0])):
    #     print()

    for c in range(columns):
        for r in range(rows):
            # print does not return object, assignment to 'array' not needed
            print((new_list[r][c]), end=" ")
        print()

    # no value being returned, explicit 'return' not needed
    # return array

Produces:

>>> array2(3, 4)
Z Z Z 
_ Z Z 
_ _ Z 
_ _ _