Having an arbitrary 2d array, say of zeros, and an array of indices:
z = np.zeros((5,5))
ix = np.array([1,4,2,3,0])
How could I add a 1
from the columns specified by a 1d array onwards, in order to obtain:
array([[0, 1, 1, 1, 1],
[0, 0, 0, 0, 1],
[0, 0, 1, 1, 1],
[0, 0, 0, 1, 1],
[1, 1, 1, 1, 1]])
I have not been able to find a simple way of doing so using numpy
.
One way would be -
In [50]: ncols = 5
In [51]: (ix[:,None] <= np.arange(ncols)).view('i1')
Out[51]:
array([[0, 1, 1, 1, 1],
[0, 0, 0, 0, 1],
[0, 0, 1, 1, 1],
[0, 0, 0, 1, 1],
[1, 1, 1, 1, 1]], dtype=int8)
If you have to add to an existing array z
-
z += (ix[:,None] <= np.arange(ncols))
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