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numpy.mask_indices(n, mask_func, k=0)[source] -
Return the indices to access (n, n) arrays, given a masking function.
Assume
mask_funcis a function that, for a square array a of size(n, n)with a possible offset argumentk, when called asmask_func(a, k)returns a new array with zeros in certain locations (functions liketriuortrildo precisely this). Then this function returns the indices where the non-zero values would be located.Parameters: n : int
The returned indices will be valid to access arrays of shape (n, n).
mask_func : callable
A function whose call signature is similar to that of
triu,tril. That is,mask_func(x, k)returns a boolean array, shaped likex.kis an optional argument to the function.k : scalar
An optional argument which is passed through to
mask_func. Functions liketriu,triltake a second argument that is interpreted as an offset.Returns: indices : tuple of arrays.
The
narrays of indices corresponding to the locations wheremask_func(np.ones((n, n)), k)is True.See also
Notes
New in version 1.4.0.
Examples
These are the indices that would allow you to access the upper triangular part of any 3x3 array:
1>>> iu=np.mask_indices(3, np.triu)For example, if
ais a 3x3 array:1234567>>> a=np.arange(9).reshape(3,3)>>> aarray([[0,1,2],[3,4,5],[6,7,8]])>>> a[iu]array([0,1,2,4,5,8])An offset can be passed also to the masking function. This gets us the indices starting on the first diagonal right of the main one:
1>>> iu1=np.mask_indices(3, np.triu,1)with which we now extract only three elements:
12>>> a[iu1]array([1,2,5])
numpy.mask_indices()
2025-01-10 15:47:30
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