Incrementing values in 2d array?

Question

I'm attempting to increment the values in a 2d array for a game I'm making, but I'm getting the same value in each array instead. This is the code:

def matrix(grid):

    nrows = len(grid)
    ncols = len(grid[0])

    for i in range(nrows):
        for j in range(ncols):
            grid[i][j] += 10

    for row in grid:
        print(row)

rows = 4
cols = 4
grid = [[0 for i in range(cols)] for i in range(rows)]
matrix(grid)

The output is:

[10, 10, 10, 10]
[10, 10, 10, 10]
[10, 10, 10, 10]
[10, 10, 10, 10]

Where as I would like it to be

[10, 20, 30, 40]
[10, 20, 30, 40]
[10, 20, 30, 40]
[10, 20, 30, 40]

Also, is it possible to stagger and use two nested for loops to provide incremented values for each row? Such as:

[10, 20, 30, 40]
[20, 40, 60, 80]
[10, 20, 30, 40]
[20, 40, 60, 80]

Snowflake Fairy · Accepted Answer · 2013-11-21 06:58:19Z

5

The output is as expected: the following line of code adds 10 to each cell, and since each is zero on entry, it becomes 10 in output

for i in range(nrows):
    for j in range(ncols):
        grid[i][j] += 10

Maybe the following would do, depending on what you are trying to do

for i in range(nrows):
    for j in range(ncols):
        grid[i][j] += 10*(j+1)

And for the two-loop version (not the output you give, but I didn't find the pattern)

for i in range(nrows):
    for j in range(ncols):
        grid[i][j] += 10*(i+j+1)

answered Nov 21, 2013 at 6:58

Snowflake Fairy

512 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

aIKid Over a year ago

Welcome to SO, Nice answer!

Leonardo · Accepted Answer · 2013-11-21 07:04:56Z

1

You might try this loop:

for i in range(nrows):
    for j in range(ncols):
        if (i % 2 != 0):
            grid[i][j] += 20*(j+1)
        else:
            grid[i][j] += 10*(j+1)

for the output:

[10, 20, 30, 40]
[20, 40, 60, 80]
[10, 20, 30, 40]
[20, 40, 60, 80]

answered Nov 21, 2013 at 7:04

Leonardo

1,5283 gold badges15 silver badges26 bronze badges

1 Comment

user2909869 Over a year ago

Interesting, exactly what I was looking for.

thefourtheye · Accepted Answer · 2013-11-21 07:09:46Z

1

Whenever you have to modify the whole list, try to do this with comprehensions. It is efficient. So, your problem can be solved with list comprehensions like this

rows = 4
cols = 4
grid = [[0] * cols for _ in range(rows)]
print [[(i * 10) for i in xrange(1, len(row) + 1)] for row in grid]

Output

[[10, 20, 30, 40], [10, 20, 30, 40], [10, 20, 30, 40], [10, 20, 30, 40]]

answered Nov 21, 2013 at 7:09

thefourtheye

241k53 gold badges466 silver badges505 bronze badges

Comments

VIKASH JAISWAL · Accepted Answer · 2013-11-21 06:59:36Z

0

You need to change your code to:

for i in range(nrows):
    val = 10
    for j in range(ncols):            
        grid[i][j] = val
        val += 10

answered Nov 21, 2013 at 6:59

VIKASH JAISWAL

8381 gold badge5 silver badges12 bronze badges

1 Comment

Leonardo Over a year ago

Or simply grid[i][j] = 10*(j+1)

uhs · Accepted Answer · 2013-11-21 07:02:40Z

0

def matrix(grid):

nrows = len(grid)
ncols = len(grid[0])
grid[0][0]=10;
for i in range(nrows):
    for j in range(ncols):
if(j!=0)
      grid[i][j] = grid[i][j-1]+10;
else 
grid[i][j]=10;

for row in grid:
    print(row)

answered Nov 21, 2013 at 7:02

uhs

8481 gold badge7 silver badges23 bronze badges

Collectives™ on Stack Overflow

Incrementing values in 2d array?

5 Answers 5

1 Comment

1 Comment

Comments

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

1 Comment

1 Comment

Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related