Direct way to generate sum of all parallel diagonals in Numpy / Pandas?

Question

I have a rectangular (can\'t be assumed to be square) Pandas DataFrame of numbers. Say I pick a diagonal direction (either \"upperleft to lowerright\" or \"upperright to lowerl

Answer 1

You may be looking for numpy.trace(), documented here, to get the trace directly, or numpy.diagonal() to get the diagonal vector, documented here

First, convert your dataframe to a numpy matrix using rectdf.as_matrix()

Then:

np.trace(matrix, offset)

The offset, which can be either positive or negative, does the shifting you require.

For example, if we do:

a = np.arange(15).reshape(5, 3)
for x in range(-4, 3): print np.trace(a, x)

We get output:

12
22
30
21
12
6
2

To do this for a general matrix, we want the range from -(rows - 1) to columns, i.e. if we have a variable rows and a variable columns:

a = np.arange(rows * columns).reshape(rows, columns)
for x in range(-(rows - 1), columns): print np.trace(a, x)