如何在python中删除数组的最后一列

Question

My array size is unknown and I would like to remove the very last column

a = np.array([["A1","A2","A3"],["B1","B2","B3"],["C1","C2","C3"]])

I have tried

a[-1:]

but it deleted all rows except the last row

I also tried

a[:-1]

and it deleted the last row.

How can I delete the last column?

Answer 1

I suggest you to read the docs aboutBasic Slicing and Indexing the numpy array.

Try this:

arr = a[:, :-1] #--> first two columns of array

Note 1: The resulting array arr of the slicing operation is just a view inside the original array a , no copy is created. If you change any entity inside the arr , this change will also be propagated in the array a and vice-a-versa.

For Example, Changing the value of arr[0, 0] will also change the corresponding value of a[0, 0] .

---

Note 2: If you want to create a new array, while removing the last column so that changes in one array should not be propagated in other array, you can use numpy.delete which returns a new array with sub-arrays along an axis deleted.

arr = np.delete(a, -1, axis=1) # --> returns new array

---

Output of >>> arr :

[['A1' 'A2']
 ['B1' 'B2']
 ['C1' 'C2']]

Answer 2

Try this:

import numpy as np
a = np.array([["A1","A2","A3"],["B1","B2","B3"],["C1","C2","C3"]])
print(a)

b = np.delete(a, np.s_[-1:], axis=1)
print(b)

Output:

[['A1' 'A2' 'A3']
 ['B1' 'B2' 'B3']
 ['C1' 'C2' 'C3']]

[['A1' 'A2']
 ['B1' 'B2']
 ['C1' 'C2']]

Answer 3

If you wish to delete the last column

b = a[:,:2]
'''array([['A1', 'A2'],
   ['B1', 'B2'],
   ['C1', 'C2']], dtype='<U2')'''

if you wish to delete the last row

c = a[:2]
'''array([['A1', 'A2', 'A3'],
   ['B1', 'B2', 'B3']], dtype='<U2'''