While learning Python for data science, a dictionary is defined as a collection of unordered data values. Unlike other data types, Dictionary holds a key: value pair. This makes the dictionary more optimized. Each key-value pair in Python are separated by colon(:) and the keys are separated by a comma.
A python dictionary is similar to a standard dictionary which we use. The dictionary should contain keys that are unique and immutable (strings, tuples, integers), and the key values can be duplicated and of any type.
Important point- Polymorphism is prohibited in keys in a dictionary.
Creation of a Dictionary:
Placement of sequence of elements within curly braces {} with comma as a separator leads to the creation of a dictionary. As already discussed earlier, a dictionary has a key and a pair of key: value. Values are mutable, but keys are immutable and non-repeatable.
Built-in function dict() can be used for the creation of a dictionary. Two curly braces {} can be used to create an empty dictionary.
Point to remember while working in python for data science - Keys in a dictionary are case sensitive, i.e. same name with different cases will be treated as two distinct keys.
# Creating an empty Dictionary
Dict = {}
print(“Empty Dictionary: “)
print(Dict)
# Creating a Dictionary
#with Integer Keys
Dict = {1: ‘Python’, 2: ‘Is’, 3: ‘Best’}
print(“\nDictionary using Integer Keys: “)
print(Dict)
#Creating a Dictionary
# with Mixed keys
Dict = {‘Name’: ‘PST’, 1: [1, 2, 3, 4]}
print(“\nDictionary using Mixed Keys: “)
print(Dict)
#Creation of Dictionary
#using dict() method
Dict = dict({1: ‘Python’, 2: ‘Is’, 3:’Best’})
print(“\nDictionary using dict(): “)
print(Dict)
# Creating a Dictionary
#with each item as a Pair
Dict = dict([(1, ‘PST’), (2, ‘Analytics’)])
print(“\nDictionary using each item as a pair: “)
print(Dict)
Output:
Empty Dictionary:
{}
Dictionary using Integer Keys:
{1: ‘Python’, 2: ‘Is’, 3: ‘Best’}
Dictionary using Mixed Keys:
{1: [1, 2, 3, 4], ‘Name’: ‘PST’}
Dictionary with the use of dict():
{1: ‘Python’, 2: ‘Is’, 3: ‘Best’}
Dictionary with each item as a pair:
{1: ‘PST’, 2: ‘Analytics’}
Nested Dictionary:
# Creating a Nested Dictionary
#as shown in the below image
Dict = {1: ‘PST’, 2: ‘For’,
3:{‘A’ : ‘Welcome’, ‘B’ : ‘To’, ‘C’ : ‘PST’}}
print(Dict)
Output:
{1: ‘PST’, 2: ‘For’, 3: {‘A’: ‘Welcome’, ‘B’: ‘To’, ‘C’: ‘PST’}}
Adding Elements to a Dictionary:
There are multiple ways to add elements in a dictionary. We can add elements one by one by defining value along with the key( dict[Key] = ‘Value’. To alter or update an existing value, use the function update(). We can add nested key values to an already existing dictionary.
Point to remember while working on python for data science- While adding a value if we add a value which already exists it will get updated or else a new key is created containing the new value.
# Creating an empty Dictionary
Dict = {}
print(“Empty Dictionary: “)
print(Dict)
# Adding elements one at a time
Dict[0] = ‘PST’
Dict[2] = ‘For’
ict[3] = 1
print(“\nDictionary after adding 3 elements: “)
print(Dict)
# Adding set of values
# to a single Key
Dict[‘Value_set’] = 2, 3, 4
print(“\nDictionary after adding 3 elements: “)
print(Dict)
# Updating existing Key’s Value
Dict[2] = ‘Analytics’
print(“\nUpdated key value: “)
print(Dict)
# Adding Nested Key value to Dictionary
Dict[5] = {‘Nested’ :{‘1’ : ‘Life’, ‘2’ : ‘Python’}}
print(“\nAdding a Nested Key: “)
print(Dict)
Output:
Empty Dictionary:
{}
Dictionary after adding 3 elements:
{0: ‘PST’, 2: ‘For’, 3: 1}
Dictionary after adding 3 elements:
{0: ‘PST’, 2: ‘For’, 3: 1, ‘Value_set’: (2, 3, 4)}
Updated key value:
{0: ‘PST’, 2: ‘Analytics’, 3: 1, ‘Value_set’: (2, 3, 4)}
Adding a Nested Key:
{0: ‘Geeks’, 2: ‘Analytics’, 3: 1, 5: {‘Nested’: {‘1’: ‘Life’, ‘2’: ‘Python’}}, ‘Value_set’: (2, 3, 4)}
Accessing Elements from Dictionary:
Key name can be used to access items from a dictionary. Keys are used inside square brackets to access items. Another way of accessing items is to use the get() function.
# Accesing an element from a Dictionary
# Creating a Dictionary
Dict = {1: ‘PST’, ‘name’: ‘For’, 3: ‘Python’}
# accessing a element using key
print(“Acessing a element using key:”)
print(Dict[‘name’])
# accessing a element using key
print(“Acessing a element using key:”)
print(Dict[1])
# accessing a element using get()
# method
print(“Acessing a element using get:”)
print(Dict.get(3))
Output:
Acessing a element using key:
For
Acessing a element using key:
PST
Acessing a element using get:
Python
Removing Elements in Dictionary:
The del() function can be used to delete keys from a dictionary in python for data science. The function del() can be used to either delete a specific key or the entire dictionary. The pop() and popitem() functions can be used to delete either specific or random keys from a dictionary. Another important function clear() can be used to clear up the whole dictionary. In the case of a nested dictionary we should provide the nested key and the particular key both to be deleted from the dictionary.
Extra point: del dict() can be used to remove the whole dictionary. Printing a deleted dictionary will generate an error.
# Initial Dictionary
Dict = { 5 : ‘Welcome’, 6 : ‘To’, 7 : ‘PST’,
‘A’ : {1 : ‘PST’, 2 : ‘For’, 3 : ‘Python’},
‘B’ : {1 : ‘Python’, 2 : ‘Life’}}
print(“Initial Dictionary: “)
print(Dict)
# Deleting a Key value
del Dict[6]
print(“\nDeleting a specific key: “)
print(Dict)
# Deleting a Key from
# Nested Dictionary
del Dict[‘A’][2]
print(“\nDeleting a key from Nested Dictionary: “)
print(Dict)
# Deleting a Key
# using pop()
Dict.pop(5)
print(“\nPopping specific element: “)
print(Dict)
# Deleting an arbitrary Key-value pair
# using popitem()
Dict.popitem()
print(“\nPops an arbitrary key-value pair: “)
print(Dict)
# Deleting entire Dictionary
Dict.clear()
print(“\nDeleting Entire Dictionary: “)
print(Dict)
Output:
Initial Dictionary:
{‘A’: {1: ‘PST’, 2: ‘For’, 3: ‘Python’}, ‘B’: {1: ‘Python’, 2: ‘Life’}, 5: ‘Welcome’, 6: ‘To’, 7: ‘PST’}
Deleting a specific key:
{‘A’: {1: ‘PST’, 2: ‘For’, 3: ‘Python’}, ‘B’: {1: ‘Python’, 2: ‘Life’}, 5: ‘Welcome’, 7: ‘PST’}
Deleting a key from Nested Dictionary:
{‘A’: {1: ‘PST’, 3: ‘Python’}, ‘B’: {1: ‘Python’, 2: ‘Life’}, 5: ‘Welcome’, 7: ‘PST’}
Popping specific element:
{‘A’: {1: ‘PST’, 3: ‘Python’}, ‘B’: {1: ‘Python’, 2: ‘Life’}, 7: ‘Geeks’}
Pops an arbitrary key-value pair:
{‘B’: {1: ‘Python’, 2: ‘Life’}, 7: ‘PST’}
Deleting Entire Dictionary:
{}
Methods in Dictionary: