ValueError: all the input arrays must have same number of dimensions

Question

I\'m having a problem with np.append.

I\'m trying to duplicate the last column of 20x361 matrix n_list_converted by using the code below:

Answer 1

The reason why you get your error is because a "1 by n" matrix is different from an array of length n.

I recommend using hstack() and vstack() instead. Like this:

import numpy as np
a = np.arange(32).reshape(4,8) # 4 rows 8 columns matrix.
b = a[:,-1:]                    # last column of that matrix.

result = np.hstack((a,b))       # stack them horizontally like this:
#array([[ 0,  1,  2,  3,  4,  5,  6,  7,  7],
#       [ 8,  9, 10, 11, 12, 13, 14, 15, 15],
#       [16, 17, 18, 19, 20, 21, 22, 23, 23],
#       [24, 25, 26, 27, 28, 29, 30, 31, 31]])

Notice the repeated "7, 15, 23, 31" column. Also, notice that I used a[:,-1:] instead of a[:,-1]. My version generates a column:

array([[7],
       [15],
       [23],
       [31]])

Instead of a row array([7,15,23,31])

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Edit: append() is much slower. Read this answer.