Python Remove brackets from arrays [duplicate]

Question

I have a list that contains many arrays.

coef

[array([[1.72158862]]),
 array([[3.28338167]]),
 array([[3.28004542]]),
 array([[6.04194548]])]

Put it into dataframe gives:

azone = pd.DataFrame(
    {'zone': zone,
     'coef': coef
    })

    zone    coef
0   1   [[1.7215886175218464]]
1   2   [[3.283381665861124]]

I wonder if there are ways to remove brackets. I tried tolist() but not giving me a result.

Also for another list:

value

[[array([8.46565297e-294, 1.63877641e-002]),
 array([1.46912451e-220, 2.44570170e-003]),
 array([3.80589351e-227, 4.41242801e-004])]

I want to have only keep the second value. desire output is:

   value
0  1.63877641e-002
1  2.44570170e-003
2  4.41242801e-004

Answer 1

Using Ravel:

coef = [np.array([[1.72158862]]),
        np.array([[3.28338167]]),
        np.array([[3.28004542]]),
        np.array([[6.04194548]])]

coef = np.array(coef).ravel()

print(coef)

array([1.72158862, 3.28338167, 3.28004542, 6.04194548])

Furthermore, if you're not going to modify the returned 1-d array, I suggest you use numpy.ravel, since it doesn't make a copy of the array, but just return a view of the array, which is much faster than numpy.flatten

Answer 2

You can use NumPy's flatten method to extract a one-dimensional array from your list of multi-dimensional arrays. For example:

coef = [np.array([[1.72158862]]),
        np.array([[3.28338167]]),
        np.array([[3.28004542]]),
        np.array([[6.04194548]])]

coef = np.array(coef).flatten()

print(coef)

array([1.72158862, 3.28338167, 3.28004542, 6.04194548])

Since NumPy arrays underly Pandas dataframes, you will find your Pandas coef series will now be of dtype float and contain only scalars.