compare the row and column in a list using python function

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Python - Algorithm to determine if a list is symmetric

I need help writing a Python function - symmetric,that takes as input a list of size n(which is a square matrix) that checks the first row is the same as the first column, the second row is the same as the second column and so on, and returns boolean True if the elements are the same and false if they are not. The list could contain integers or strings.

def symmetric(my_list):

my_list = [[1, 2, 3],
           [2, 3, 4],
           [3, 4, 1]]

Is this homework? Try posting some of your attempts before asking us to do your task for you — inspectorG4dget, Jul 05 '12 at 22:54
Hi, This is what I have tried so far and I get a sytax error message: — Fadyboy, Jul 06 '12 at 09:15
Hi, this is what I have tried so far: def symmetric(p): size = len(p) i = 0 while i < size: j = 0 while j < size if p[i][j] != p[j][i] return False j = j + 1 i = i + 1 return True I get a syntax error message — Fadyboy, Jul 06 '12 at 09:23

John La Rooy · Answer 1 · 2012-07-06T00:56:14.067

This works in Python2

my_list == map(list, zip(*my_list))

zip(*some_2d_list) is a fairly well known idiom, when some_2d_list is unpacked and processed by zip it has the effect of transposing the rows and columns

Unfortunately zip returns a list of tuples, so it is necessary to convert those to lists. This is what map(list, ...) does

It may appear wasteful as testing for equality will compare each pair that are not on the diagonal twice, but this is done at the C level, so will be much faster than using explicit loops and doing the minimum number of comparisons.

If it is homework, I'd suggest that you should probably use nested loops

EDIT: In Python3, map(...) returns a map object, you can get the Python2 behaviour by using list(map(...))

EDIT: I think in Python3, this is better

all(i==j for i,*j in zip(my_list ,*my_list))

+1, you can add an edit about python 3.x: `map()` returns a map object in python 3.x, so the comparison will return `False` in python 3.x — Ashwini Chaudhary, Jul 05 '12 at 23:27
@AshwiniChaudhary, I thought of a neater way to do it in Python3 — John La Rooy, Jul 06 '12 at 00:56

score 0 · Answer 2 · answered Jul 05 '12 at 23:15

0

import numpy as np
# convert the 2d list into an ndarry
x = np.array(my_list)
# test if x is identical to its transpose
isSymmetric = (x.T == x).all()

isSymmetric then tells you the result.

answered Jul 05 '12 at 23:15

nye17

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compare the row and column in a list using python function

2 Answers2