Remove or replace matrix in python

user_10818418 0
Viewed 66

Hi i have this matrix

e.g

import numpy as np
a= np.arange(9).reshape(3, 3)

[[1. 2. 3. ]
 [4. 5. 6. ]
 [7. 8. 9. ]]

how do i delete the bottomost value of a selected col (e.g col = 1) and the rest of the values on top gets pushed down, and if there is an empty space, put "0"

so the matrix becomes

[[1. 0. 3. ]
 [4. 2. 6. ]
 [7. 5. 9. ]]
numpy python
3 Answers

Roll the second column and then set the first element of the column to zero

a = np.arange(1,10).reshape(3, 3)

a[:, 1] = np.roll(a[:, 1], 1)
a[0, 1] = 0

print(a)

Output:

[[1 0 3]
 [4 2 6]
 [7 5 9]]
user_104786610

I suggest you may use np.pad here:

E.g.

>>> import numpy as np
>>> a= np.arange(1, 10).reshape(3, 3)
>>> print a
[[1 2 3]
 [4 5 6]
 [7 8 9]]
>>> a[:,1] = np.pad(a[:,1], pad_width=1, mode='constant')[:a.shape[1]]
>>> print a
[[1 0 3]
 [4 2 6]
 [7 5 9]]
user_56633150 
In [215]: a = np.arange(1,10).reshape(3,3)

Make a temporary array to hold the new column's values:

In [216]: temp = np.zeros(a.shape[0],a.dtype)                                   
In [217]: temp[1:] = a[:-1,1]

copy that into a:

In [218]: a[:,1] = temp                                                         
In [219]: a                                                                     
Out[219]: 
array([[1, 0, 3],
       [4, 2, 6],
       [7, 5, 9]])
user_9019250
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