numpy.triu_indices_from — NumPy v2.2 Manual (original) (raw)

numpy.triu_indices_from(arr, k=0)[source]#

Return the indices for the upper-triangle of arr.

See triu_indices for full details.

Parameters:

arrndarray, shape(N, N)

The indices will be valid for square arrays.

kint, optional

Diagonal offset (see triu for details).

Returns:

triu_indices_fromtuple, shape(2) of ndarray, shape(N)

Indices for the upper-triangle of arr.

Examples

Create a 4 by 4 array

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]])

Pass the array to get the indices of the upper triangular elements.

triui = np.triu_indices_from(a) triui (array([0, 0, 0, 0, 1, 1, 1, 2, 2, 3]), array([0, 1, 2, 3, 1, 2, 3, 2, 3, 3]))

a[triui] array([ 0, 1, 2, 3, 5, 6, 7, 10, 11, 15])

This is syntactic sugar for triu_indices().

np.triu_indices(a.shape[0]) (array([0, 0, 0, 0, 1, 1, 1, 2, 2, 3]), array([0, 1, 2, 3, 1, 2, 3, 2, 3, 3]))

Use the k parameter to return the indices for the upper triangular array from the k-th diagonal.

triuim1 = np.triu_indices_from(a, k=1) a[triuim1] array([ 1, 2, 3, 6, 7, 11])