CODEWITHSUNDEEP
pythondictionaryfor-loopset
Waterploof
Waterploof

Reputation: 101

Delete the value of a dictionary if the value is the key in python

I have a dictionary and I want to delete each value of the dictionary which is the key. I want this output: G = {'y': {'z'}, 'z': {'u', 'f', 'y'}, 'u': {'z'}}

G = {'y': {'z', 'y'}, 'z': {'z', 'u', 'f', 'y'}, 'u': {'u', 'z'}}

I tried this but I know. It's wrong.

for key,value in G.items():
    if key == value:
        del value

Upvotes: 2

Views: 85

Answers (2)

jpp
jpp

Reputation: 164693

You aren't modifying the dictionary, but a variable value. In addition, you don't want to look for equality of keys and values, you want to check if your key is in your set value. Then remove it from your set via set.remove. So you can use:

for key, value in G.items():
    if key in value:
        G[key].remove(key)

print(G)

{'y': {'z'}, 'z': {'u', 'y', 'f'}, 'u': {'z'}}

Alternatively, you can use set.discard, which doesn't give KeyError if the value does not exist in your set. The if condition may therefore be omitted.

for key, value in G.items():
    G[key].discard(key)

Finally, consider the below dictionary comprehension, which creates a new dictionary and assigns it to G. This is not intrinsically inefficient: time complexity will be the same as the above methods. This version uses set.difference, here via its syntactic sugar -:

G = {k: v - {k} for k, v in G.items()}

As per @JonClements' comment, a one-line version which maintains references to G is possible via dict.update:

G.update({k: v - {k} for k, v in G.items()})

Upvotes: 4

gilch
gilch

Reputation: 11671

Delete the key in the value, not the value itself.

for key, value in G.items():
    if key in value:
        value.remove(key)

Upvotes: 0

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