How do I delete a row in a numpy array which contains a zero? [duplicate]

Question

I'm trying to write a function to delete all rows in which have a zero value in. This is not from my code, but an example of the idea I am using:

import numpy as np
a=np.array(([7,1,2,8],[4,0,3,2],[5,8,3,6],[4,3,2,0]))
b=[]

for i in range(len(a)):
    for j in range (len(a[i])):
        if a[i][j]==0:
            b.append(i)

print 'b=', b
for zero_row in b:
    x=np.delete(a,zero_row, 0)

print 'a=',a

and this is my output:

b= [1, 3]
a= [[7 1 2 8]
 [4 0 3 2]
 [5 8 3 6]
 [4 3 2 0]]

How do I get rid of the rows with the index in b? Sorry, I'm fairly new to this any help would be really appreciated.

Answer 1

I'm trying to write a function to delete all rows in which have a zero value in.

You don't need to write a function for that, it can be done in a single expression:

>>> a[np.all(a != 0, axis=1)]
array([[7, 1, 2, 8],
       [5, 8, 3, 6]])

Read as: select from a all rows that are entirely non-zero.

Answer 2

Looks like np.delete does't change the array, just returns a new array, so

Instead of

x = np.delete(a,zero_row, 0)

try

a = np.delete(a,zero_row, 0)

Answer 3

I think I have found the answer:

as @tuxcanfly said I changed x to a. Also I have now removed the for loop as it removed the row with index 2 for some reason.

Instead I now just chose to delete the rows using b as the delete function with use the elements in the list to remove the row with that index.

the new code:

import numpy as np
a=np.array(([7,1,2,8],[4,0,3,2],[5,8,3,6],[4,3,2,0]))
b=[]

for i in range(len(a)):
    for j in range (len(a[i])):
        if a[i][j]==0:
            b.append(i)
print 'b=',b
for zero_row in b:
    a=np.delete(a,b, 0)

print 'a=',a

and the output:

b= [1, 3]
a= [[7 1 2 8]
 [5 8 3 6]]