Create a list with certain number of rows and columns in Python

Question

I have a problem I can't seem to get right.

I have 2 numbers, A & B. I need to make a list of A rows with B columns, and have them print out 'R0CO', 'R0C1', etc.

Code:

import sys

A= int(sys.argv[1])

B= int(sys.argv[2])

newlist = []
row = A
col = B
for x in range (0, row): 
  newlist.append(['R0C' + str(x)])

  for y in range(0, col):
    newlist[x].append('R1C' + str(y))

print(newlist)

This is not working. The following is the output I get and the expected output: Program Output

Program Failed for Input: 2 3 Expected Output:

[['R0C0', 'R0C1', 'R0C2'], ['R1C0', 'R1C1', 'R1C2']]

Your Program Output:

[['R0C0', 'R1C0', 'R1C1', 'R1C2'], ['R0C1', 'R1C0', 'R1C1', 'R1C2']]

Your output was incorrect. Try again

Thank you for editing my question, Patrick. I have only been programming for three weeks, and just joined this site the other day. Still learning. — Wolverine39
– Wolverine39, Commented Nov 21, 2017 at 20:32
You should be appending in only one place, the innermost for loop. You should also be making the row numbers in the strings programmatically, not hardcoding R0C. Look at this page for some techniques for formatting python strings — Patrick Haugh
– Patrick Haugh, Commented Nov 21, 2017 at 20:35
@PatrickHaugh They still need to append a new list on each iteration of the outer loop, though — Alex von Brandenfels
– Alex von Brandenfels, Commented Nov 21, 2017 at 20:36
@AlexvonBrandenfels Good point. Maybe better to say that the strings should only be added in the innermost loop — Patrick Haugh
– Patrick Haugh, Commented Nov 21, 2017 at 20:38

Sefe · Accepted Answer · 2017-11-21 20:41:00Z

5

You are first adding R0Cx and then R1Cxy. You need to add RxCy. So try:

newlist = []
row = A
col = B
for x in range (0, row): 
  newlist.append([])

  for y in range(0, col):
    newlist[x].append('R' + str(x) + 'C' + str(y))

print(newlist)

answered Nov 21, 2017 at 20:41

Sefe

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3 Comments

Wolverine39 Over a year ago

Perfect!! I was getting close, but just saw this. Can you explain real quick why we use empty brackets for the first append?

Sefe Over a year ago

It‘s for adding an empty array you can fill in the second loop. Otherwise you would have nothing to fill.

Wolverine39 Over a year ago

Got it. I figured it out after thinking about it, but thank you for your reply!

Elis Byberi · Accepted Answer · 2017-11-21 20:36:21Z

0

You have to fill columns in a row while still in that row:

rows = []
row = 2
col = 3

for x in range(0, row):
    columns = []
    for y in range(0, col):
        columns.append('R' + str(x) + 'C' + str(y))

    rows.append(columns)


print(rows)

will print:

[['R0C0', 'R0C1', 'R0C2'], ['R1C0', 'R1C1', 'R1C2']]

answered Nov 21, 2017 at 20:36

Elis Byberi

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Comments

Greg Mueller · Accepted Answer · 2017-11-21 20:44:18Z

0

Try changing your range commands as shown:

for x in range (row): 
  for y in range(col):

In fact, you have a second issue that you are not modifying the text properly:

newlist = []
row = A
col = B
for x in range (row):   
    sublist = []
    for y in range(col):
        sublist.append('R{}C{}'.format(x, y))
    newlist.append(sublist)

edited Nov 21, 2017 at 20:44

answered Nov 21, 2017 at 20:35

Greg Mueller

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2 Comments

Patrick Haugh Over a year ago

This way is obviously cleaner, but functionally identical.

Greg Mueller Over a year ago

That's true, the real issue is with the way you are looping.

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