numpy矩陣。將所有0移動到每一行的末尾

Question

給定python numpy中的矩陣，其中有一些行，前導零。我需要將全部零移到行尾。 例如

0 2 3 4 
0 0 1 5 
2 3 1 1 

應轉化爲

2 3 4 0 
1 5 0 0 
2 3 1 1 

有什麼好方法在python numpy的做到這一點？

Answer 1

要解決的前導零行 -

def fix_leading_zeros(a): 
    mask = a!=0 
    flipped_mask = mask[:,::-1] 
    a[flipped_mask] = a[mask] 
    a[~flipped_mask] = 0 
    return a 

爲推動全零行到後面 -

def push_all_zeros_back(a): 
    # Based on http://stackoverflow.com/a/42859463/3293881 
    valid_mask = a!=0 
    flipped_mask = valid_mask.sum(1,keepdims=1) > np.arange(a.shape[1]-1,-1,-1) 
    flipped_mask = flipped_mask[:,::-1] 
    a[flipped_mask] = a[valid_mask] 
    a[~flipped_mask] = 0 
    return a 

樣品試驗 -

In [220]: a 
Out[220]: 
array([[0, 2, 3, 4], 
     [0, 0, 1, 5], 
     [2, 3, 1, 1]]) 

In [221]: fix_leading_zero_rows(a) 
Out[221]: 
array([[2, 3, 4, 0], 
     [1, 5, 0, 0], 
     [2, 3, 1, 1]]) 

In [266]: a 
Out[266]: 
array([[0, 2, 3, 4, 0], 
     [0, 0, 1, 5, 6], 
     [2, 3, 0, 1, 0]]) 

In [267]: push_all_zeros_back(a) 
Out[267]: 
array([[2, 3, 4, 0, 0], 
     [1, 5, 6, 0, 0], 
     [2, 3, 1, 0, 0]]) 

Answer 2

前導零，簡單的循環

ar = np.array([[0, 2, 3, 4], 
     [0, 0, 1, 5], 
     [2, 3, 1, 1]])  

for i in range(ar.shape[0]): 
    for j in range(ar.shape[1]): # prevent infinite loop if row all zero 
     if ar[i,0] == 0: 
      ar[i]=np.roll(ar[i], -1) 
ar 
Out[31]: 
array([[2, 3, 4, 0], 
     [1, 5, 0, 0], 
     [2, 3, 1, 1]])