如何将文本文件中的值存储到 2D Numpy 数组中？

Question

I have a dataset on a txt file with 373 rows and 3 columns.My teacher asked me to create 2 arrays.The 'array1' stores all the rows of the dataset that their third column has the value 1,and the 'array2' stores every row that has number 2 at column2. The arrays must be numpy arrays. I tried 'class1 = np.zeros(len(dataset)).reshape(len(dataset)//3,3)' but i was getting the error message: 'ValueError: cannot reshape array of size 373 into shape (124,3)' I tried all different kinds of variations. But i couldnt find a way to make a 2D work.I only managed to store the column number1 with on both arrays with this code:

'''
import numpy as np

dataset = np.loadtxt("first_attempt_dataset.txt")

class1 = np.zeros(len(dataset))
class2 = np.zeros(len(dataset))


for i in range(0,len(dataset)): 
  if dataset[i,2] == 1:  
    class1[i] = dataset[i][1]
  elif dataset[i,2] == 2:
    class2[i] = dataset[i][1]


class1 = class1[class1 != 0]  #delete the remained zeros from declaration
class2 = class2[class2 != 0]  

'''

How can i store every column instead of only 1?

Answer 1

I feel you misunderstand the question from your teacher. The question is "...The 'array1' stores all the rows of the dataset that their third column has the value 1,...", so I would do this:

import numpy as np

a = np.array([[1,2,3], [3,2,1], [2,3,1], [2,1,3], [3,1,2]])
b = a[a[:,2]==1]
print(b)

result is:

[[3 2 1]
 [2 3 1]]

Similar to the second half of the question, you need to change the column number to 1 .

Hope this helps.