numpy.diag_indices#
- numpy.diag_indices(n, ndim=2)[source]#
Return the indices to access the main diagonal of an array.
This returns a tuple of indices that can be used to access the main diagonal of an array a with
a.ndim >= 2
dimensions and shape (n, n, …, n). Fora.ndim = 2
this is the usual diagonal, fora.ndim > 2
this is the set of indices to accessa[i, i, ..., i]
fori = [0..n-1]
.- Parameters:
- nint
The size, along each dimension, of the arrays for which the returned indices can be used.
- ndimint, optional
The number of dimensions.
See also
Examples
>>> import numpy as np
Create a set of indices to access the diagonal of a (4, 4) array:
>>> di = np.diag_indices(4) >>> di (array([0, 1, 2, 3]), array([0, 1, 2, 3])) >>> a = np.arange(16).reshape(4, 4) >>> a array([[ 0, 1, 2, 3], [ 4, 5, 6, 7], [ 8, 9, 10, 11], [12, 13, 14, 15]]) >>> a[di] = 100 >>> a array([[100, 1, 2, 3], [ 4, 100, 6, 7], [ 8, 9, 100, 11], [ 12, 13, 14, 100]])
Now, we create indices to manipulate a 3-D array:
>>> d3 = np.diag_indices(2, 3) >>> d3 (array([0, 1]), array([0, 1]), array([0, 1]))
And use it to set the diagonal of an array of zeros to 1:
>>> a = np.zeros((2, 2, 2), dtype=int) >>> a[d3] = 1 >>> a array([[[1, 0], [0, 0]], [[0, 0], [0, 1]]])