如何根据条件更新多个字典值？

Question

I have a dictionary which looks like:

dict = {'A':[1,2], 'B':[0], 'c':[4]}

need it to look like:

dict = {'A':[1,2], 'B':[0,0], 'c':[4,0]}

What I am doing right now:

dict = {x: y+[0] for (x,y) in dict.items() if len(y) < 2}

which generates:

dict = {'B':[0,0], 'c':[4,0]}

any idea how I could avoid eliminating those who do not meet the condition?

Answer 1

You're almost there. Try:

my_dict = {x: y + [0] if len(y) < 2 else y
           for (x,y) in dict.items()}

(as mentioned by jp_data_analysis, avoid naming variables after builtins like dict )

Answer 2

This is one way.

Note : do not name variables after classes, eg use d instead of dict .

d = {'A':[1,2], 'B':[0], 'c':[4]}

d = {k: v if len(v)==2 else v+[0] for k, v in d.items()}

# {'A': [1, 2], 'B': [0, 0], 'c': [4, 0]}

Answer 3

You can use dictionary comprehension:

d = {'A':[1,2], 'B':[0], 'c':[4]}
new_d = {a:b+[0] if len(b) == 1 else b for a, b in d.items()}

Also, it is best practice not to assign variables to names shadowing common builtins, such as dict , as you are then overriding the function in the current namespace.

Answer 4

1. Your code is almost correct. Your problem is that you're filtering out any lists bigger than 2 . What you need to do instead is simply place them in the new dictionary unchanged. This can be done using the ternary operator . It has the form value1 if condition else value2 .

2. Also, if you want a more general way to pad every list in your dictionary to be of equal length, you can use map and max .

Here is your code with the above modifications:

>>> d = {'A':[1, 2], 'B': [0], 'c': [4]}
>>> 
>>> max_len = max(map(len, d.values()))
>>> {k: v + [0] * (max_len - len(v)) if len(v) < max_len else v for k, v in d.items()}
{'A': [1, 2], 'B': [0, 0], 'c': [4, 0]}
>>> 

Answer 5

A generalized way:

d = {'A':[1,2], 'B':[0], 'c':[4]}

m = max(len(v) for v in d.values())
for k, v in d.items():
    if len(v) < m:
        d[k].extend([0 for i in range(m-len(v))])

Answer 6

You were very close, just use update() :

d = {'A':[1,2], 'B':[0], 'c':[4]}

d.update({x: y+[0] for (x,y) in d.items() if len(y) < 2})

d
# {'A': [1, 2], 'B': [0, 0], 'c': [4, 0]}

Like others have said, don't use reassign reserved names like dict , it's a one way street down to debugging hell.