np.array 用于变量矩阵

Question

import numpy as np

 data = np.array([[10, 20, 30, 40, 50, 60, 70, 80, 90],
    [2, 7, 8, 9, 10, 11],
    [3, 12, 13, 14, 15, 16],
    [4, 3, 4, 5, 6, 7, 10, 12]],dtype=object)

target = data[:,0]

It has this error.

---

 IndexError     Traceback (most recent call last)

       Input In \[82\], in \<cell line: 9\>()

 data =  np.array(\[\[10, 20, 30, 40, 50, 60, 70, 80, 90\],

       \[2, 7, 8, 9, 10, 11\],
\[3, 12, 13, 14, 15, 16\],
\[4, 3, 4, 5, 6, 7, 10,12\]\],dtype=object)

  # Define the target data ----\> 9 target = data\[:,0\]

   IndexError: too many indices for array: array is 1-dimensional, but 2 were indexed

May I know how to fix it, please? I mean do not change the elements in the data. Many thanks. I made the matrix in the same size and the error message was gone. But I have the data with variable size.

Answer 1

You have a array of objects, so you can't use indexing on axis=1 as there is none ( data.shape -> (4,) ).

Use a list comprehension:

out = np.array([a[0] for a in data])

Output: array([10, 2, 3, 4])