Can NumPy's flatten() return a 2D array?
I applied flatten() on an array of shape (12L, 54L), and I got a new array of shape (1L, 648L). Is that supposed to happen from time to time? If so, in which cases does that happen?
I use NumPy 1.9.2.
asked Nov 17, 2015 at 18:55
Franck Dernoncourt
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1 Answer
Unlike NumPy arrays, NumPy matrices are always 2D objects. So calling flatten on a NumPy matrix returns another 2D matrix, albeit one with shape (1, N):
In [112]: x = np.matrix(np.random.randint(10, size=(12,54))) In [116]: x.shape Out[116]: (12, 54) In [117]: x.flatten().shape Out[117]: (1, 648) If you convert the matrix to an array, then flatten will return a 1D array:
In [125]: np.asarray(x).flatten().shape Out[125]: (648,) 
1 Comment
Franck Dernoncourt
Thanks, good catch, the issue was indeed it was a matrix, not an array. I should have converted the matrix to an array first (Numpy matrix to array), or directly use numpy.matrix.A1.