CODEWITHSUNDEEP
python
fredrik
fredrik

Reputation: 10281

How to remove dictionary's keys and values based on another dictionary?

I wish to remove keys and values in one JSON dictionary based on another JSON dictionary's keys and values. In a sense I am looking perform a "subtraction". Let's say I have JSON dictionaries a and b:

a =  {
     "my_app":
        {
        "environment_variables":
           {
            "SOME_ENV_VAR":
                [
                "/tmp",
                "tmp2"
                ]
           },

        "variables":
           { "my_var": "1",
             "my_other_var": "2"
           }
        }
     }

b =  {
      "my_app":
        {
        "environment_variables":
           {
            "SOME_ENV_VAR":
                [
                "/tmp"
                ]
           },

        "variables":
           { "my_var": "1" }
        }
     }

Imagine you could do a-b=c where c looks like this:

c =  {
       "my_app":
       {
        "environment_variables":
           {
            "SOME_ENV_VAR":
                [
                "/tmp2"
                ]
           },

        "variables":
           { "my_other_var": "2" }
       }
     }

How can this be done?

Upvotes: 1

Views: 2037

Answers (3)

rhlobo
rhlobo

Reputation: 1336

The following does what you need:

    def subtract(a, b):
        result = {}

        for key, value in a.items():
            if key not in b or b[key] != value:
                if not isinstance(value, dict):
                    if isinstance(value, list):
                        result[key] = [item for item in value if item not in b[key]]
                    else:
                        result[key] = value
                    continue

                inner_dict = subtract(value, b[key])
                if len(inner_dict) > 0:
                    result[key] = inner_dict

        return result

It checks if both key and value are present. It could del items, but I think is much better to return a new dict with the desired data instead of modifying the original.

   c = subtract(a, b)

UPDATE

I have just updated for the latest version of the data provided by in the question. Now it 'subtract' list values as well.

UPDATE 2

Working example: ipython notebook

Upvotes: 0

soupault
soupault

Reputation: 6510

The way you can do it is to:

  1. Create copy of a -> c;
  2. Iterate over every key, value pair inside b;
  3. Check if for same top keys you have same inner keys and values and delete them from c;
  4. Remove keys with empty values.

You should modify code, if your case will be somehow different (no dict(dict), etc).

print(A)
print(B)
C = A.copy()

# INFO: Suppose your max depth is as follows: "A = dict(key:dict(), ...)"
for k0, v0 in B.items():
    # Look for similiar outer keys (check if 'vars' or 'env_vars' in A)
    if k0 in C:
        # Look for similiar inner (keys, values)
        for k1, v1 in v0.items():
            # If we have e.g. 'my_var' in B and in C and values are the same
            if k1 in C[k0] and v1 == C[k0][k1]:
                del C[k0][k1]
        # Remove empty 'vars', 'env_vars'
        if not C[k0]:
            del C[k0]

print(C)

{'environment_variables': {'SOME_ENV_VAR': ['/tmp']}, 
 'variables': {'my_var': '2', 'someones_var': '1'}}

{'environment_variables': {'SOME_ENV_VAR': ['/tmp']},
 'variables': {'my_var': '2'}}

{'variables': {'someones_var': '1'}}

Upvotes: 0

magnetometer
magnetometer

Reputation: 656

You can loop through your dictionary using for key in dictionary: and you can delete keys using del dictionary[key], I think that's all you need. See the documentation for dictionaries: https://docs.python.org/2/tutorial/datastructures.html#dictionaries

Upvotes: 1

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