How to replace diagonals with zero?

Python
#1

I need help with the syntax to replace the diagonal elements of a matrix with zero in Python. Can anyone please provide code examples or guidance on how to achieve this? Thank you.

import pandas as pd
import numpy as np

# create a sample DataFrame
df = pd.DataFrame({'a': [1, 2, 3], 'b': [4, 5, 6], 'c': [7, 8, 9]})

# convert the DataFrame to a NumPy array
arr = df.values.reshape((3, 2))

# replace both diagonals of the array with zeros
np.fill_diagonal(arr, 0)
np.fill_diagonal(np.fliplr(arr), 0)

# convert the array back to a DataFrame
df = pd.DataFrame(arr, columns=df.columns, index=df.index)
df

ValueError: cannot reshape array of size 9 into shape (3,2)
#2

There is a simple technique of replacing both your diagonals with 0, it involves using the for loop for iterating over the dataframe and then using the indexing technique to replace the indexes of the diagonal. Here is the code for it:

  • The for loop is used to iterate over the indices of each row of the dataframe using the range() function and the length of the dataframe.
  • For each row, the first diagonal element is accessed using the index i, i and the second diagonal element is accessed using the index i, len(df) - i - 1. Both of these elements are then replaced with zeros.