CODEWITHSUNDEEP
python
rahul2001
rahul2001

Reputation: 1657

Accessing columns in a matrix in Python

I am trying to create a simple tictactoe game and am trying to save the rows to a row[] and columns to a columns[] so that I can access each element in the board by doing board[row][col].

I am getting the rows saved when traversing thru the matrix in the first loop but unable to save the column indices. Any thoughts on what im doing wrong and how to do it correctly?

Heres the code:

board = [ 
            ['|', '|', '|' ],
            ['|', '|', '|'],
            ['|', '|', '|'] 
        ] 

row = []
col = []

def tictactoe ():

    # print('\n'.join([''.join(['{:4}'.format(item) for item in row]) for row in board]))

    for i in range(0,len(board)):
        row.append(board[i])
        for j in (0, len(board)):
            col.append(board[j])


    print(row, '!!!!!')
    print(col)

Upvotes: 0

Views: 1492

Answers (3)

Cristian Lupascu
Cristian Lupascu

Reputation: 40516

In addition to Fernando's answer explaining what went wrong in your approach and how to solve it, here's how you can achieve the same thing in a simplified manner:

def tictactoe():
    rows = board # board is already an array containing the rows.
    cols = zip(*board)

    print(rows)
    print(cols)

Upvotes: 0

Fernando Jorge Mota
Fernando Jorge Mota

Reputation: 1554

Try

board = [ 
            ['|', '|', '|' ],
            ['|', '|', '|'],
            ['|', '|', '|'] 
        ] 

row = []
col = []

def tictactoe ():

    # print('\n'.join([''.join(['{:4}'.format(item) for item in row]) for row in board]))

    for i in range(0,len(board)):
        row.append(board[i])
        for j in range(0, len(board[i])):
            col.append(board[i][j])


    print(row, '!!!!!')
    print(col)

Basically in your example you're always acessing only the items of your board list (i.e the rows), to access a item of a list inside the board list (i.e the columns), you need to access first the list inside of the boards array (using board[i], for example), and after this you'll complete with the item you want to access, board[i][j], for example.

A suggestion is, instead of using for i in range(0, len(board)), use directly the list iterator, as this: for i in board. In this case, i will not be an integer, but the element of the board variable that you're accessing. Your code will become something like this:

board = [ 
            ['|', '|', '|' ],
            ['|', '|', '|'],
            ['|', '|', '|'] 
        ] 

row = []
col = []

def tictactoe ():

    # print('\n'.join([''.join(['{:4}'.format(item) for item in row]) for row in board]))

    for i in board:
        row.append(i)
        for j in i:
            col.append(j)


    print(row, '!!!!!')
    print(col)

Note that the syntax for accessing columns change too: Instead of using board[i][j], we just use for j in i, and the j variable will contains the column value itself. (as i is the row contained in board variable)

Upvotes: 2

tarun_2709
tarun_2709

Reputation: 21

You forgot range while iterating columns in the following line:

for j in (0, len(board)):

Upvotes: 0

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