Problems counting zeroes standing at the beginning of rows in a matrix-CodePudding

In Python I have tried to use the code below to fill a list with occurences of zeroes in rows of a matrix. These 0 must stand before all the non zero-numbers: for example in a row like [0,0,3,0] I would count only the first two zeroes.

occurence_of_zeroes=[0]*dim
for i in range(dim):
   for j in range(dim):
      while matrix[i][j]==0:
         occurence_of_zeroes[i]=occurence_of_zeroes[i] 1
   print("In row ",i 1," there are ",occurence_of_zeroes[i]," zeroes at the beginning")
print("Is this working?")

when I try to execute the code with previously defined dim and matrix, the console never spits out the result and freezes. Why?

CodePudding user response：

you can use NumPy arr it have build-in function

In [3]: arr
Out[3]: 
array([[1, 2, 0, 3],
      [3, 9, 0, 4]])

In [4]: np.count_nonzero(arr==0)
Out[4]: 2

In [5]:def func_cnt():
            for arr in arrs:
                zero_els = np.count_nonzero(arr==0)
                # here, it counts the frequency of zeroes actually

CodePudding user response：

You are reaching an infinite loop in that while because inside it you don't update any variable for it's condition

I assume what you want is something like below.

matrix = [
    [0, 2, 3],
    [0, 0, 3],
    [0, 1, 0],
]
dim = 3 # 3 rows 3 columns I suppose
occurence_of_zeroes=[[] for _ in range(dim)]
for i in range(dim):
    j = 0
    while matrix[i][j]==0:
        occurence_of_zeroes[i].append(j)
        j =1

print(occurence_of_zeroes)
"""
[
    [0], 
    [0, 1], 
    [0]
]
"""

CodePudding user response：

while matrix[i][j]==0:
     occurence_of_zeroes[i]=occurence_of_zeroes[i] 1

is an infinite loop. Simply use if statement instead.

occurence_of_zeroes=[0]*dim
for i in range(dim):
   for j in range(dim):
      if matrix[i][j]==0:
         occurence_of_zeroes[i]=occurence_of_zeroes[i] 1
   print("In row ",i 1," there are ",occurence_of_zeroes[i]," zeroes at the beginning")
print("Is this working?")

CodePudding user response：

The problem is that you don't exit the while loop to increment j. Here's a fix to your code.

occurence_of_zeroes=[0]*dim
for i in range(dim):
    for j in range(dim):
        if matrix[i][j]!=0:
            break    
        occurence_of_zeroes[i]=occurence_of_zeroes[i] 1
    print("In row ",i 1," there are ",occurence_of_zeroes[i]," zeroes at the beginning")
print("Is this working?")