numpy.ravel

numpy.ravel(a, order='C')

Return a flattened array.

A 1-D array, containing the elements of the input, is returned. A copy is made only if needed.

Parameters:

a : array_like

Input array. The elements in a are read in the order specified by order, and packed as a 1-D array.

order : {‘C’,’F’, ‘A’, ‘K’}, optional

The elements of a are read using this index order. ‘C’ means to index the elements in C-like order, with the last axis index changing fastest, back to the first axis index changing slowest. ‘F’ means to index the elements in Fortran-like index order, with the first index changing fastest, and the last index changing slowest. Note that the ‘C’ and ‘F’ options take no account of the memory layout of the underlying array, and only refer to the order of axis indexing. ‘A’ means to read the elements in Fortran-like index order if a is Fortran contiguous in memory, C-like order otherwise. ‘K’ means to read the elements in the order they occur in memory, except for reversing the data when strides are negative. By default, ‘C’ index order is used.

Returns:

1d_array : ndarray

Output of the same dtype as a, and of shape (a.size,).

See also

ndarray.flat

1-D iterator over an array.

ndarray.flatten

1-D array copy of the elements of an array in row-major order.

Notes

In C-like (row-major) order, in two dimensions, the row index varies the slowest, and the column index the quickest. This can be generalized to multiple dimensions, where row-major order implies that the index along the first axis varies slowest, and the index along the last quickest. The opposite holds for Fortran-like, or column-major, index ordering.

Examples

It is equivalent to reshape(-1, order=order).

>>> x = np.array([[1, 2, 3], [4, 5, 6]])
>>> print np.ravel(x)
[1 2 3 4 5 6]

>>> print x.reshape(-1)
[1 2 3 4 5 6]

>>> print np.ravel(x, order='F')
[1 4 2 5 3 6]

When order is ‘A’, it will preserve the array’s ‘C’ or ‘F’ ordering:

>>> print np.ravel(x.T)
[1 4 2 5 3 6]
>>> print np.ravel(x.T, order='A')
[1 2 3 4 5 6]

When order is ‘K’, it will preserve orderings that are neither ‘C’ nor ‘F’, but won’t reverse axes:

>>> a = np.arange(3)[::-1]; a
array([2, 1, 0])
>>> a.ravel(order='C')
array([2, 1, 0])
>>> a.ravel(order='K')
array([2, 1, 0])

>>> a = np.arange(12).reshape(2,3,2).swapaxes(1,2); a
array([[[ 0,  2,  4],
        [ 1,  3,  5]],
       [[ 6,  8, 10],
        [ 7,  9, 11]]])
>>> a.ravel(order='C')
array([ 0,  2,  4,  1,  3,  5,  6,  8, 10,  7,  9, 11])
>>> a.ravel(order='K')
array([ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11])