Question

I have a nx1 array, a:

array([[0],
       [0],
       [0]])

when I slice it with

a[:-1,0]

it becomes:

a([0,0])

and I’m not able to use it in plot (now the dimensions are wrong, even though the length is correct). I’ve tried

a[:-1,0].T

and

transpose(a[:-1,0])

to no avail.

How do I slice without changing the shape? (I want to keep it in column form)

Answer 1

Say a = numpy.zeros((3,1)) , then

    b = a[:-1,:]

will give you a column vector.

    array([[ 0.],
           [ 0.]])

When slicing a numpy array, you have to distinguish between adressing the content of a column, e.g. a[:,0], and adressing the column itself, e.g. a[:,0:1] or – in this case – a[:,:].