CODEWITHSUNDEEP
pythonpython-3.xdictionary
Sayanta Seth
Sayanta Seth

Reputation: 77

Delete dictionary values if they are present in a set

I have a Python set

A = {34, 4, 7, 39, 40, 13, 18, 20}

and a dictionary

B = {4: [6, 34, 39], 7: [18, 34], 13: [6, 18, 34], 18: [7, 13], 
     20: [31, 47], 34: [4, 7, 13], 39: [4, 8], 40: [15, 43]}

I want to create a new dictionary C such that if any of the values in B contains a number in A, then they must be removed from the corresponding value list. Keys should be unaffected.

For example, the desired output that I am looking for is:

C = {4: [6], 7: [], 13: [6], 18: [], 20: [31, 47], 34: [], 39: [8]}

I tried to solve this using the following code:

C = {}
for key, value in B_mod.items():
    if value in A:
        C[key] = value
print("C is:", C)

The output that I am getting is as follows:

C is: {7: 18, 18: 7, 34: 4, 39: 4}

Clearly, it is not working.

*Please note that B_mod means that I am unlisting the list in values of dictionary B using the code:

B_mod = {k:v[0] for k,v in B.items()} # Unlisitng the values of dictionary B

I did this because I could not iterate through lists as values in B.*

Any help to get C?

Upvotes: 1

Views: 68

Answers (3)

Lionel Foxcroft
Lionel Foxcroft

Reputation: 1737

You can do it in one line with this dictionary and list comprehension:

C = {k: [x for x in v if x not in A] for k, v in B.items()}

Upvotes: 1

Selcuk
Selcuk

Reputation: 59315

You can use a combination of a dictionary and list comprehensions:

>>> {k: [i for i in v if i not in A] for k, v in B.items()}
{4: [6], 7: [], 13: [6], 18: [], 20: [31, 47], 34: [], 39: [8], 40: [15, 43]}

Upvotes: 1

juanpa.arrivillaga
juanpa.arrivillaga

Reputation: 96172

You definitely can iterate through the lists in the values of B, indeed, you need to, so something like this:

>>> A = {34, 4, 7, 39, 40, 13, 18, 20}
>>> B = {4: [6, 34, 39], 7: [18, 34], 13: [6, 18, 34], 18: [7, 13], 20: [31, 47], 34: [4, 7, 13], 39: [4, 8], 40: [15, 43]}
>>> C = {}
>>> for key, value in B.items():
...     new_value = []
...     for val in value:
...         if val not in A:
...             new_value.append(val)
...     C[key] = new_value
...
>>> C
{4: [6], 7: [], 13: [6], 18: [], 20: [31, 47], 34: [], 39: [8], 40: [15, 43]}
>>>

You can also use a dictionary comprehension with a list comprehension:

>>> {k:[v for v in vs if v not in A] for k, vs in B.items()}
{4: [6], 7: [], 13: [6], 18: [], 20: [31, 47], 34: [], 39: [8], 40: [15, 43]}

Which is the equivalent of the for-loop approach. Whichever makes more sense to you is fine.

Upvotes: 2

Related Questions