Assigning to columns in NumPy

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Use a[:,1] = x[:,0]. You need x[:,0] to select the column of x as a single numpy array. If you have the choice of how to format x, it’s better to not make it a 2-dimensional array in the first place, but just a regular (row) array:

>>> a
array([[ 0.,  0.,  0.],
       [ 0.,  0.,  0.],
       [ 0.,  0.,  0.],
       [ 0.,  0.,  0.],
       [ 0.,  0.,  0.]])
>>> x = numpy.ones(5)
>>> x
array([ 1.,  1.,  1.,  1.,  1.])
>>> a[:,1] = x
>>> a
array([[ 0.,  1.,  0.],
       [ 0.,  1.,  0.],
       [ 0.,  1.,  0.],
       [ 0.,  1.,  0.],
       [ 0.,  1.,  0.]])

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