I am using numpy. I have a matrix with 1 column and N rows and I want to get an array from with N elements.
For example, if i have M = matrix([[1], [2], [3], [4]]), I want to get A = array([1,2,3,4]).
To achieve it, I use A = np.array(M.T)[0]. Does anyone know a more elegant way to get the same result?
Thanks!
ravel() and flatten() functions from numpy are two techniques that I would try here. I will like to add to the posts made by Joe, Siraj, bubble and Kevad.
Ravel:
A = M.ravel()
print A, A.shape
>>> [1 2 3 4] (4,)
Flatten:
M = np.array([[1], [2], [3], [4]])
A = M.flatten()
print A, A.shape
>>> [1 2 3 4] (4,)
numpy.ravel() is faster, since it is a library level function which does not make any copy of the array. However, any change in array A will carry itself over to the original array M if you are using numpy.ravel().
numpy.flatten() is slower than numpy.ravel(). But if you are using numpy.flatten() to create A, then changes in A will not get carried over to the original array M.
numpy.squeeze() and M.reshape(-1) are slower than numpy.flatten() and numpy.ravel().
%timeit M.ravel()
>>> 1000000 loops, best of 3: 309 ns per loop
%timeit M.flatten()
>>> 1000000 loops, best of 3: 650 ns per loop
%timeit M.reshape(-1)
>>> 1000000 loops, best of 3: 755 ns per loop
%timeit np.squeeze(M)
>>> 1000000 loops, best of 3: 886 ns per loop