Numpy: Fix array with rows of different lengths by filling the empty elements with zeros

Solution 1:

This could be one approach -

def numpy_fillna(data):
    # Get lengths of each row of data
    lens = np.array([len(i) for i in data])

    # Mask of valid places in each row
    mask = np.arange(lens.max()) < lens[:,None]

    # Setup output array and put elements from data into masked positions
    out = np.zeros(mask.shape, dtype=data.dtype)
    out[mask] = np.concatenate(data)
    return out

Sample input, output -

In [222]: # Input object dtype array
     ...: data = np.array([[1, 2, 3, 4],
     ...:                  [2, 3, 1],
     ...:                  [5, 5, 5, 5, 8 ,9 ,5],
     ...:                  [1, 1]])

In [223]: numpy_fillna(data)
Out[223]: 
array([[1, 2, 3, 4, 0, 0, 0],
       [2, 3, 1, 0, 0, 0, 0],
       [5, 5, 5, 5, 8, 9, 5],
       [1, 1, 0, 0, 0, 0, 0]], dtype=object)

Solution 2:

You could use pandas instead of numpy:

In [1]: import pandas as pd

In [2]: df = pd.DataFrame([[1, 2, 3, 4],
   ...:                    [2, 3, 1],
   ...:                    [5, 5, 5, 5],
   ...:                    [1, 1]], dtype=float)


In [3]: df.fillna(0.0).values
Out[3]: 
array([[ 1.,  2.,  3.,  4.],
       [ 2.,  3.,  1.,  0.],
       [ 5.,  5.,  5.,  5.],
       [ 1.,  1.,  0.,  0.]])

Solution 3:

use np.pad().

In [62]: arr
Out[62]: 
[array([0]),
 array([83, 74]),
 array([87, 61, 23]),
 array([71,  3, 81, 77]),
 array([20, 44, 20, 53, 60]),
 array([54, 36, 74, 35, 49, 54]),
 array([11, 36,  0, 98, 29, 87, 21]),
 array([ 1, 22, 62, 51, 45, 40, 36, 86]),
 array([ 7, 22, 83, 58, 43, 59, 45, 81, 92]),
 array([68, 78, 70, 67, 77, 64, 58, 88, 13, 56])]

In [63]: max_len = np.max([len(a) for a in arr])

In [64]: np.asarray([np.pad(a, (0, max_len - len(a)), 'constant', constant_values=0) for a in arr])
Out[64]: 
array([[ 0,  0,  0,  0,  0,  0,  0,  0,  0,  0],
       [83, 74,  0,  0,  0,  0,  0,  0,  0,  0],
       [87, 61, 23,  0,  0,  0,  0,  0,  0,  0],
       [71,  3, 81, 77,  0,  0,  0,  0,  0,  0],
       [20, 44, 20, 53, 60,  0,  0,  0,  0,  0],
       [54, 36, 74, 35, 49, 54,  0,  0,  0,  0],
       [11, 36,  0, 98, 29, 87, 21,  0,  0,  0],
       [ 1, 22, 62, 51, 45, 40, 36, 86,  0,  0],
       [ 7, 22, 83, 58, 43, 59, 45, 81, 92,  0],
       [68, 78, 70, 67, 77, 64, 58, 88, 13, 56]])