user3078618 user3078618 - 2 months ago 34
Python Question

Get diagonal without using numpy in Python

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
I need to get the diagonal that goes from left-> right, top-> bottom

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

Thanks.

jez jez
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)]