CODEWITHSUNDEEP
pythonmultidimensional-array
Mohan Kumar sajja moka
Mohan Kumar sajja moka

Reputation: 87

Matrix multiplication in python giving error, How can I overcome this?

I am trying to print the following pattern:

3 3 3 3 3
3 2 2 2 3
3 2 1 2 3
3 2 2 2 3
3 3 3 3 3

My python code is:

def pattern(n):
    d = n + (n - 1)
    l = [[0 for row in range(d)] for col in range(d)]
    for a in range(0, n):
        for i in range(a, d):
            for j in range(a, d):
                l[a][i][j].append(n)
        d -= 1
        n -= 1


print(pattern(3))

But I am getting the following Error:

Traceback (most recent call last):
File "test.py", line 10, in <module>
  print(pattern(3))
File "test.py", line 7, in pattern
  l[a][i][j].append(n)
TypeError: 'int' object is not subscriptable

Can anyone guide me how to overcome this?

Thank you in advance.

Upvotes: 0

Views: 121

Answers (2)

AKX
AKX

Reputation: 169032

Because it's somewhat hard to understand how your code is supposed to do what it should (sorry!), here's a pretty Pythonic way to generate a matrix like this as a generator function.

def pattern(n):
    size = n * 2 - 1
    n_1 = n - 1
    for y in range(size):
        yield [max(abs(x - n_1), abs(y - n_1)) + 1 for x in range(size)]

The idea is that we look at the "distance" of the cell we're generating from n - 1, which must be the center point of the grid (which is n * 2 - 1 items wide and tall).

As it's a generator function, you can get a list-of-lists out of it by calling e.g. list(pattern(size)).

Here's an example program –

for size in range(1, 6):
    print(size)
    for row in pattern(size):
        print(row)

– and its output:

1
[1]
2
[2, 2, 2]
[2, 1, 2]
[2, 2, 2]
3
[3, 3, 3, 3, 3]
[3, 2, 2, 2, 3]
[3, 2, 1, 2, 3]
[3, 2, 2, 2, 3]
[3, 3, 3, 3, 3]
4
[4, 4, 4, 4, 4, 4, 4]
[4, 3, 3, 3, 3, 3, 4]
[4, 3, 2, 2, 2, 3, 4]
[4, 3, 2, 1, 2, 3, 4]
[4, 3, 2, 2, 2, 3, 4]
[4, 3, 3, 3, 3, 3, 4]
[4, 4, 4, 4, 4, 4, 4]
5
[5, 5, 5, 5, 5, 5, 5, 5, 5]
[5, 4, 4, 4, 4, 4, 4, 4, 5]
[5, 4, 3, 3, 3, 3, 3, 4, 5]
[5, 4, 3, 2, 2, 2, 3, 4, 5]
[5, 4, 3, 2, 1, 2, 3, 4, 5]
[5, 4, 3, 2, 2, 2, 3, 4, 5]
[5, 4, 3, 3, 3, 3, 3, 4, 5]
[5, 4, 4, 4, 4, 4, 4, 4, 5]
[5, 5, 5, 5, 5, 5, 5, 5, 5]

EDIT: As requested in comments, here's a simplified version which is not a generator function and doesn't use list comprehensions:

def pattern_simple(n):
    size = n * 2 - 1
    n_1 = n - 1
    rows = []
    for y in range(size):
        row = []
        for x in range(size):
            row.append(max(abs(x - n_1), abs(y - n_1)) + 1)
        rows.append(row)
    return rows

Upvotes: 4

Serge Ballesta
Serge Ballesta

Reputation: 148965

Just to start from your own code even if the answer is a bit late...

You code tries to build an array of 0, and then writes decreasing values in sub-array. Simply you wrongly copied it. It should be:

def pattern(n):
    d = n + (n - 1)
    l = [[0 for row in range(d)] for col in range(d)]
    for a in range(0, n):
        for i in range(a, d):
            for j in range(a, d):
                l[i][j]=n
        n -= 1
        d -= 1
    return l

Upvotes: 1

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