diff options
Diffstat (limited to 'numpy/core/numeric.py')
| -rw-r--r-- | numpy/core/numeric.py | 59 |
1 files changed, 45 insertions, 14 deletions
diff --git a/numpy/core/numeric.py b/numpy/core/numeric.py index e72ab3012..55e6c1cad 100644 --- a/numpy/core/numeric.py +++ b/numpy/core/numeric.py @@ -1139,7 +1139,7 @@ def roll(a, shift, axis=None): array([8, 9, 0, 1, 2, 3, 4, 5, 6, 7]) >>> np.roll(x, -2) array([2, 3, 4, 5, 6, 7, 8, 9, 0, 1]) - + >>> x2 = np.reshape(x, (2,5)) >>> x2 array([[0, 1, 2, 3, 4], @@ -1606,11 +1606,11 @@ little_endian = (sys.byteorder == 'little') @set_module('numpy') -def indices(dimensions, dtype=int): +def indices(dimensions, dtype=int, sparse=False): """ Return an array representing the indices of a grid. - Compute an array where the subarrays contain index values 0,1,... + Compute an array where the subarrays contain index values 0, 1, ... varying only along the corresponding axis. Parameters @@ -1619,28 +1619,38 @@ def indices(dimensions, dtype=int): The shape of the grid. dtype : dtype, optional Data type of the result. + sparse : boolean, optional + Return a sparse representation of the grid instead of a dense + representation. Default is False. + + .. versionadded:: 1.17 Returns ------- - grid : ndarray - The array of grid indices, - ``grid.shape = (len(dimensions),) + tuple(dimensions)``. + grid : one ndarray or tuple of ndarrays + If sparse is False: + Returns one array of grid indices, + ``grid.shape = (len(dimensions),) + tuple(dimensions)``. + If sparse is True: + Returns a tuple of arrays, with + ``grid[i].shape = (1, ..., 1, dimensions[i], 1, ..., 1)`` with + dimensions[i] in the ith place See Also -------- - mgrid, meshgrid + mgrid, ogrid, meshgrid Notes ----- - The output shape is obtained by prepending the number of dimensions - in front of the tuple of dimensions, i.e. if `dimensions` is a tuple - ``(r0, ..., rN-1)`` of length ``N``, the output shape is - ``(N,r0,...,rN-1)``. + The output shape in the dense case is obtained by prepending the number + of dimensions in front of the tuple of dimensions, i.e. if `dimensions` + is a tuple ``(r0, ..., rN-1)`` of length ``N``, the output shape is + ``(N, r0, ..., rN-1)``. The subarrays ``grid[k]`` contains the N-D array of indices along the ``k-th`` axis. Explicitly:: - grid[k,i0,i1,...,iN-1] = ik + grid[k, i0, i1, ..., iN-1] = ik Examples -------- @@ -1665,15 +1675,36 @@ def indices(dimensions, dtype=int): Note that it would be more straightforward in the above example to extract the required elements directly with ``x[:2, :3]``. + If sparse is set to true, the grid will be returned in a sparse + representation. + + >>> i, j = np.indices((2, 3), sparse=True) + >>> i.shape + (2, 1) + >>> j.shape + (1, 3) + >>> i # row indices + array([[0], + [1]]) + >>> j # column indices + array([[0, 1, 2]]) + """ dimensions = tuple(dimensions) N = len(dimensions) shape = (1,)*N - res = empty((N,)+dimensions, dtype=dtype) + if sparse: + res = tuple() + else: + res = empty((N,)+dimensions, dtype=dtype) for i, dim in enumerate(dimensions): - res[i] = arange(dim, dtype=dtype).reshape( + idx = arange(dim, dtype=dtype).reshape( shape[:i] + (dim,) + shape[i+1:] ) + if sparse: + res = res + (idx,) + else: + res[i] = idx return res |