How to convert ndarray to array?

Question

I'm using pandas.Series and np.ndarray.

The code is like this

>>> t
array([[ 0.,  0.,  0.],
       [ 0.,  0.,  0.],
       [ 0.,  0.,  0.]])
>>> pandas.Series(t)
Exception: Data must be 1-dimensional
>>>

And I trie to convert it into 1-dimensional array:

>>> tt = t.reshape((1,-1))
>>> tt
array([[ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.]])

tt is still multi-dimensional since there are double '['.

So how do I get a really convert ndarray into array?

After searching, it says they are the same. However in my situation, they are not working the same.

Daniel · Accepted Answer · 2013-08-13 03:26:41Z

40

An alternative is to use np.ravel:

>>> np.zeros((3,3)).ravel()
array([ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.])

The importance of ravel over flatten is ravel only copies data if necessary and usually returns a view, while flatten will always return a copy of the data.

To use reshape to flatten the array:

tt = t.reshape(-1)

edited Aug 13, 2013 at 3:26

answered Aug 13, 2013 at 3:17

Daniel

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Comments

nneonneo · Accepted Answer · 2013-08-13 03:23:53Z

6

Use .flatten:

>>> np.zeros((3,3))
array([[ 0.,  0.,  0.],
       [ 0.,  0.,  0.],
       [ 0.,  0.,  0.]])
>>> _.flatten()
array([ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.])

EDIT: As pointed out, this returns a copy of the input in every case. To avoid the copy, use .ravel as suggested by @Ophion.

edited Aug 13, 2013 at 3:23

answered Aug 13, 2013 at 3:14

nneonneo

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2 Comments

Jaime Over a year ago

.flatten returns a copy, not a view, so it should generally not be your first option.

nneonneo Over a year ago

@Jaime: thanks, I've noted it. (And +1 to Ophion for pointing out .ravel...clearly I don't use NumPy enough.)

Jemshid KK · Accepted Answer · 2017-05-16 04:56:57Z

1

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

oneDvector = tt.A1

This is the only approach which solved the problem of double brackets, that is conversion to 1D array that nd matrix.

answered May 16, 2017 at 4:56

Jemshid KK

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