Creating a hot vector (numpy)

From	Paulo da Silva <p_s_d_a_s_i_l_v_a_ns@netcabo.pt>
Newsgroups	comp.lang.python
Subject	Creating a hot vector (numpy)
Date	2016-04-18 01:46 +0100
Organization	Aioe.org NNTP Server
Message-ID	<nf1aor$kiu$1@gioia.aioe.org> (permalink)

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Hi all.

I have seen this "trick" to create a hot vector.

In [45]: x
Out[45]: array([0, 1])

In [46]: y
Out[46]: array([1, 1, 1, 0, 0, 1, 0, 0], dtype=uint8)

In [47]: y[:,None]
Out[47]:
array([[1],
       [1],
       [1],
       [0],
       [0],
       [1],
       [0],
       [0]], dtype=uint8)

In [48]: x==y[:,None]
Out[48]:
array([[False,  True],
       [False,  True],
       [False,  True],
       [ True, False],
       [ True, False],
       [False,  True],
       [ True, False],
       [ True, False]], dtype=bool)

In [49]: (x==y[:,None]).astype(np.float32)
Out[49]:
array([[ 0.,  1.],
       [ 0.,  1.],
       [ 0.,  1.],
       [ 1.,  0.],
       [ 1.,  0.],
       [ 0.,  1.],
       [ 1.,  0.],
       [ 1.,  0.]], dtype=float32)

How does this (step 48) work?

Thanks

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Creating a hot vector (numpy) Paulo da Silva <p_s_d_a_s_i_l_v_a_ns@netcabo.pt> - 2016-04-18 01:46 +0100
  Re: Creating a hot vector (numpy) Reto Brunner <brunnre8@gmail.com> - 2016-04-18 04:05 +0000
    Re: Creating a hot vector (numpy) Paulo da Silva <p_s_d_a_s_i_l_v_a_ns@netcabo.pt> - 2016-04-18 16:38 +0100

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