user3078618 - 9 months ago 100

Python Question

I'm trying to get the diagonal from a matrix in Python without using numpy (i really cant use numpy). Do someone here knows how to do it?

Example of what i want to get:

`get_diagonal ([[1,2,3,4],[5,6,7,8],[9,10,11,12]], 1, 1, 1)`

Result: [1, 6, 11]

Or like:

`get_diagonal ([[1,2,3,4],[5,6,7,8],[9,10,11,12]], 1, 2, 1)`

Result: [2, 7, 12]

Until know I've tried a lot of stuff but doesn't work.

`def obter_diagonal(matrix, line, column, direc):`

d = []

if direc == 1:

for i in matrix:

for j in i:

if all(i == line, j == column):

d.extend(matrix[i][j])

else:

for i in matrix:

for j in i:

d.extend[len(matrix)-1-i][j]

return d

if

`direc==1`

if direc?? -1 need to get the diag that goes from right-> left, top->bott

Thanks.

Answer

To get the leading diagonal you could do

```
diag = [ mat[i][i] for i in range(len(mat)) ]
```

or even

```
diag = [ row[i] for i,row in enumerate(mat) ]
```

And play similar games for other diagonals. For example, for the counter-diagonal (top-right to bottom-left) you would do something like:

```
diag = [ row[-i-1] for i,row in enumerate(mat) ]
```

For other minor diagonals you would have to use `if`

conditionals in the list comprehension, e.g.:

```
diag = [ row[i+offset] for i,row in enumerate(mat) if 0 <= i+offset < len(row)]
```

Source (Stackoverflow)