Delete an Element from a Dictionary

Delete an element from a dictionary

The del statement removes an element:

del d[key]

Note that this mutates the existing dictionary, so the contents of the dictionary changes for anybody else who has a reference to the same instance. To return a new dictionary, make a copy of the dictionary:

def removekey(d, key):
    r = dict(d)
    del r[key]
    return r

The dict() constructor makes a shallow copy. To make a deep copy, see the copy module.

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Note that making a copy for every dict del/assignment/etc. means you're going from constant time to linear time, and also using linear space. For small dicts, this is not a problem. But if you're planning to make lots of copies of large dicts, you probably want a different data structure, like a HAMT (as described in this answer).

How can I remove a key from a Python dictionary?

To delete a key regardless of whether it is in the dictionary, use the two-argument form of dict.pop():

my_dict.pop('key', None)

This will return my_dict[key] if key exists in the dictionary, and None otherwise. If the second parameter is not specified (i.e. my_dict.pop('key')) and key does not exist, a KeyError is raised.

To delete a key that is guaranteed to exist, you can also use:

del my_dict['key']

This will raise a KeyError if the key is not in the dictionary.

How to delete a value from a dictionary?

I believe you are trying to remove "John" from the list stored in the dictionary. You first have to get a reference to that list, this can be done with the "Player" key. Then you can use the remove method of the list class to remove an item from it.

An example I think solves your problem is

data = {'Player': ['John','Steffen'], age: [25,26]} 
data['Player'].remove('John') # First reference the list, then remove an item from it

I'd take a guess and say the list of ages corresponds to the list of players, so you'd have to also remove John's age from there.

Best method to delete an item from a dict

• Use d.pop if you want to capture the removed item, like in item = d.pop("keyA").

• Use del if you want to delete an item from a dictionary.

• If you want to delete, suppressing an error if the key isn't in the dictionary: if thekey in thedict: del thedict[thekey]

What is the best way to remove a dictionary item by value in python?

You can use a simple dict comprehension:

myDict = {key:val for key, val in myDict.items() if val != 42}

As such:

>>> {key:val for key, val in myDict.items() if val != 42}
{8: 14, 1: 'egg'}

How to remove a KEY from a dictionary in c#

The Remove() method actually deletes an existing key-value pair from a dictionary. You can also use the clear method to delete all the elements of the dictionary.

var cities = new Dictionary<string, string>(){
    {"UK", "London, Manchester, Birmingham"},
    {"USA", "Chicago, New York, Washington"},
    {"India", "Mumbai, New Delhi, Pune"}
};

cities.Remove("UK"); // removes UK 
//cities.Remove("France"); //throws run-time exception: KeyNotFoundException

if(cities.ContainsKey("France")){ // check key before removing it
    cities.Remove("France");
}

cities.Clear(); //removes all elements

You can read this for more information https://www.tutorialsteacher.com/csharp/csharp-dictionary

Remove an item from a dictionary when its key is unknown

Be aware that you're currently testing for object identity (is only returns True if both operands are represented by the same object in memory - this is not always the case with two object that compare equal with ==). If you are doing this on purpose, then you could rewrite your code as

some_dict = {key: value for key, value in some_dict.items() 
             if value is not value_to_remove}

But this may not do what you want:

>>> some_dict = {1: "Hello", 2: "Goodbye", 3: "You say yes", 4: "I say no"}
>>> value_to_remove = "You say yes"
>>> some_dict = {key: value for key, value in some_dict.items() if value is not value_to_remove}
>>> some_dict
{1: 'Hello', 2: 'Goodbye', 3: 'You say yes', 4: 'I say no'}
>>> some_dict = {key: value for key, value in some_dict.items() if value != value_to_remove}
>>> some_dict
{1: 'Hello', 2: 'Goodbye', 4: 'I say no'}

So you probably want != instead of is not.

How to remove elements from a Python dictionary based on elements in a list?

I would use a dictionary comprehension to map the keys with the values that aren't found within a list:

new_dict = {k: v for k, v in old_dict.items() if v not in the_list} # filter from the list

Python: Remove item from dictionary in functional way

There is no built-in way for dicts, you have to do it yourself. Something to the effect of:

>>> data = dict(a=1,b=2,c=3)
>>> data
{'a': 1, 'b': 2, 'c': 3}
>>> {k:v for k,v in data.items() if k != item}

Note, Python 3.9 did add a | operator for dicts to create a new, merged dict:

>>> data
{'a': 1, 'b': 2, 'c': 3}
>>> more_data = {"b":4, "c":5, "d":6}

Then

>>> data | more_data
{'a': 1, 'b': 4, 'c': 5, 'd': 6}

So, similar to + for list concatenation. Previously, could have done something like:

>>> {**data, **more_data}
{'a': 1, 'b': 4, 'c': 5, 'd': 6}

Note, set objects support operators to create new sets, providing operators for various basic set operations:

>>> s1 = {'a','b','c'}
>>> s2 = {'b','c','d'}
>>> s1 & s2 # set intersection
{'b', 'c'}
>>> s1 | s2 # set union
{'c', 'a', 'b', 'd'}
>>> s1 - s2 # set difference
{'a'}
>>> s1 ^ s2 # symmetric difference
{'a', 'd'}

This comes down to API design choices.

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