put_along_axis(arr, indices, values, axis)
This iterates over matching 1d slices oriented along the specified axis in the index and data arrays, and uses the former to place values into the latter. These slices can be different lengths.
Functions returning an index along an axis, like argsort
and argpartition
, produce suitable indices for this function.
This is equivalent to (but faster than) the following use of ndindex
and :None:None:`s_`, which sets each of ii
and kk
to a tuple of indices:
Ni, M, Nk = a.shape[:axis], a.shape[axis], a.shape[axis+1:]
J = indices.shape[axis] # Need not equal M
for ii in ndindex(Ni):
for kk in ndindex(Nk):
a_1d = a [ii + s_[:,] + kk]
indices_1d = indices[ii + s_[:,] + kk]
values_1d = values [ii + s_[:,] + kk]
for j in range(J):
a_1d[indices_1d[j]] = values_1d[j]
Equivalently, eliminating the inner loop, the last two lines would be:
a_1d[indices_1d] = values_1d
Destination array.
Indices to change along each 1d slice of :None:None:`arr`. This must match the dimension of arr, but dimensions in Ni and Nj may be 1 to broadcast against :None:None:`arr`.
values to insert at those indices. Its shape and dimension are broadcast to match that of indices
.
The axis to take 1d slices along. If axis is None, the destination array is treated as if a flattened 1d view had been created of it.
Put values into the destination array by matching 1d index and data slices.
take_along_axis
Take values from the input array by matching 1d index and data slices
For this sample array
>>> a = np.array([[10, 30, 20], [60, 40, 50]])
We can replace the maximum values with:
>>> ai = np.expand_dims(np.argmax(a, axis=1), axis=1)
... ai array([[1], [0]])
>>> np.put_along_axis(a, ai, 99, axis=1)See :
... a array([[10, 99, 20], [99, 40, 50]])
The following pages refer to to this document either explicitly or contain code examples using this.
numpy.take_along_axis
numpy.put
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