Data Structures- Dictionaries Adopted from Stanford Unis CS106ap - - PowerPoint PPT Presentation

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Data Structures- Dictionaries Adopted from Stanford Unis CS106ap - - PowerPoint PPT Presentation

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Data Structures- Dictionaries Adopted from Stanford Unis CS106ap course slides by Kylie Jue and Sonja Johnson-Yu and Code in Place by Piech and Sahami; Koca Unis Comp125 course by Ayca Tuzmen Todays How can I organize my data so its

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Adopted from Stanford Uni’s CS106ap course slides by Kylie Jue and Sonja Johnson-Yu and Code in Place by Piech and Sahami; Koca Uni’s Comp125 course by Ayca Tuzmen

Data Structures- Dictionaries

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Today’s questions

How can I organize my data so it’s easier to use?

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How can I organize my data so it’s easier to use?

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Think/Share:

Store names of habitat animals and their corresponding diet

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elephant bear otter platypus clams grass shrimp berries

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Task - Relating data with each other

['elephant', ‘bear', ‘otter', ‘platypus'] ['grass', ‘berries', ‘clams’, ‘shrimp']

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Task - Relating data with each other

['elephant', ‘bear', ‘otter', ‘platypus'] ['grass', ‘berries', ‘clams’, ‘shrimp']

These pieces of information are linked!

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['elephant', ‘bear', ‘otter', ‘platypus'] ['grass', ‘berries', ‘clams’, ‘shrimp']

These pieces of information are linked! Can we store them so they’re associated with each other?

Task - Relating data with each other

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Dictionaries!

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Dictionary A container data type that maps “keys” to their associated “values”.

Definition

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Anatomy of a Dictionary

name_of_dic = {} name_of_dic = {'elephant': 'grass', 'bear': ‘berries', 'otter': ‘clams’, 'platypus': ‘shrimp'}

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Anatomy of a Dictionary

name_of_dic = {'elephant': 'grass', 'bear': ‘berries', 'otter': ‘clams’, 'platypus': ‘shrimp'}

This is a dictionary literal

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Anatomy of a Dictionary

name_of_dic = {'elephant': 'grass', 'bear': ‘berries', 'otter': ‘clams’, 'platypus': ‘shrimp'}

It is easier to visualize it this way:

‘elephant' ‘bear' ‘otter' ‘platypus' ‘grass’ ‘berries' ‘clams’ shrimp’ dict keys values

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Anatomy of a Dictionary

Each key can store

  • ne value

‘elephant' ‘bear' ‘otter' ‘platypus' ‘grass’ ‘berries' ‘clams' ‘shrimp’ dict keys values

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Anatomy of a Dictionary

Each key can store

  • ne value

‘elephant' ‘bear' ‘otter' ‘platypus' ‘grass’ ‘berries' ‘clams' ‘shrimp’ dict keys values

>>> d[‘elephant’]

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Anatomy of a Dictionary - Get/Set

‘elephant' ‘bear' ‘otter' ‘platypus' ‘grass’ ‘berries' ‘clams' ‘shrimp’ dict keys values

>>> d[‘elephant’]

This operation is called ‘‘get’’

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Anatomy of a Dictionary - Get/Set

‘elephant' ‘bear' ‘otter' ‘platypus' ‘grass’ ‘berries' ‘clams' ‘shrimp’ dict keys values

>>> d[‘elephant’]

This operation is called ‘‘get’’

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Anatomy of a Dictionary - Get/Set

‘elephant' ‘bear' ‘otter' ‘platypus' ‘grass’ ‘berries' ‘clams' ‘shrimp’ dict keys values

>>> d[‘elephant’] ‘grass’

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Anatomy of a Dictionary - Get/Set

‘elephant' ‘bear' ‘otter' ‘platypus' ‘grass’ ‘berries' ‘clams' ‘shrimp’ dict keys values

>>> d[‘elephant’] ‘grass’

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Anatomy of a Dictionary - Get/Set

‘elephant' ‘bear' ‘otter' ‘platypus' ‘grass’ ‘berries' ‘clams' ‘shrimp’ dict keys values

>>> d[‘elephant’] ‘grass’ >>> d[‘elephant’] = ‘leaves’

This operation is called ‘‘set’’

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Anatomy of a Dictionary - Get/Set

‘elephant' ‘bear' ‘otter' ‘platypus' ‘leaves’ ‘berries' ‘clams' ‘shrimp’ dict keys values

>>> d[‘elephant’] ‘grass’ >>> d[‘elephant’] = ‘leaves’

This operation is called ‘‘set’’

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Anatomy of a Dictionary - Get/Set

‘elephant' ‘bear' ‘otter' ‘platypus' ‘leaves’ ‘berries' ‘clams' ‘shrimp’ dict keys values

>>> d[‘elephant’] ‘grass’ >>> d[‘elephant’] = ‘leaves’ >>> d[‘cat’]

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Anatomy of a Dictionary - Get/Set

‘elephant' ‘bear' ‘otter' ‘platypus' ‘leaves’ ‘berries' ‘clams' ‘shrimp’ dict keys values

>>> d[‘elephant’] ‘grass’ >>> d[‘elephant’] = ‘leaves’ >>> d[‘cat’]

KeyError

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Anatomy of a Dictionary - Get/Set

‘elephant' ‘bear' ‘otter' ‘platypus' ‘leaves’ ‘berries' ‘clams' ‘shrimp’ dict keys values

>>> d[‘elephant’] ‘grass’ >>> d[‘elephant’] = ‘leaves’ >>> d[‘cat’]

“get” errors if the key is not in the dict

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Dictionary - in

‘elephant' ‘bear' ‘otter' ‘platypus' ‘leaves’ ‘berries' ‘clams' ‘shrimp’ dict keys values

>>>‘elephant’ in d

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Dictionary - in

‘elephant' ‘bear' ‘otter' ‘platypus' ‘leaves’ ‘berries' ‘clams' ‘shrimp’ dict keys values

>>>‘elephant’ in d True

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Dictionary - in

‘elephant' ‘bear' ‘otter' ‘platypus' ‘leaves’ ‘berries' ‘clams' ‘shrimp’ dict keys values

>>>‘elephant’ in d True >>>‘cat’ not in d True

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Dictionary - in

‘elephant' ‘bear' ‘otter' ‘platypus' ‘leaves’ ‘berries' ‘clams' ‘shrimp’ dict keys values

>>>‘elephant’ in d True >>>‘cat’ not in d True

Common pattern: Check if key is present. If it is, do something. If it isn’t, do something else.

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Building a dictionary

>>> d = {}

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Building a dictionary

>>> d = {}

Create an empty dictionary

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Building a dictionary

>>> d = {} >>> d[‘elephant’] = ‘grass’

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Building a dictionary

>>> d = {} >>> d[‘elephant’] = ‘grass’

We can add keys using ‘‘set’’

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Building a dictionary

>>> d = {} >>> d[‘elephant’] = ‘grass’ >>> d

We can add keys using ‘‘set’’

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Building a dictionary

>>> d = {} >>> d[‘elephant’] = ‘grass’ >>> d {‘elephant’: ‘grass'} We can add keys using ‘‘set’’

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Building a dictionary

>>> d = {‘elephant’: ‘grass’}

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Types of Dictionaries

  • So far, we’ve seen dictionaries mapping from strings to ints

○ This is not the only type of dictionary! ○ You can map from string/int/float to string/int/float...

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Think/Share:

Store names of CS lecturers and their ages

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Accessing a Dictionary’s Keys

>>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’}

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Building a dictionary

>>> d = {‘Ayca’: 34} >>> d[‘Ayca’] += 2

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Building a dictionary

>>> d = {‘Ayca’: 34} >>> d[‘Ayca’] += 2

we can get/set on the same line! (same as d[‘Ayca’] = d[‘Ayca] + 2)

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Building a dictionary

>>> d = {‘Ayca’: 34} >>> d[‘Ayca’] += 2 >>> d[‘Ayca’] {‘Ayca’: 36}

we can get/set on the same line! (same as d[‘Ayca’] = d[‘Ayca] + 2)

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Accessing a Dictionary’s Keys

>>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> d.keys()

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Accessing a Dictionary’s Keys

>>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> d.keys() dict_keys([‘Ayca’, ‘Nick’, ‘Ondrej’, ‘Chris’])

Iterable collection of all the keys. Iterable means it can be used in foreach

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Accessing a Dictionary’s Keys

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> list(d.keys()) [‘Ayca’, ‘Nick’, ‘Ondrej’, Chris]

we are using list() to convert d.keys() into a list

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Accessing a Dictionary’s Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’}

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Accessing a Dictionary’s Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> list(d.values())

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Accessing a Dictionary’s Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> list(d.values())

we are using list() to convert d.values() into a list

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Accessing a Dictionary’s Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> list(d.values()) [34,28,30,29]

we are using list() to convert d.values() into a list

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Looping over a Dictionary’s Keys

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’}

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Looping over a Dictionary’s Keys

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> for name in d.keys():

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Looping over a Dictionary’s Keys

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> for name in d.keys(): ... print(name)

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Looping over a Dictionary’s Keys

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> for name in d.keys(): ... print(name) Ayca Nick Ondrej Chris

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Looping over a Dictionary’s Keys

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> for name in d.keys(): ... print(name) Ayca Nick Ondrej Chris

we can use foreach on the dictionary’s keys!

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Looping over a Dictionary’s Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’}

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Looping over a Dictionary’s Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> for age in d.values():

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Looping over a Dictionary’s Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> for age in d.values(): ... print(age)

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Looping over a Dictionary’s Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> for age in d.values(): ... print(age) 34 28 30 29

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Looping over a Dictionary’s Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> for age in d.values(): ... print(age) 34 28 30 29

we can use foreach on the dictionary’s values!

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Looping over a Dictionary’s Keys and Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’}

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Looping over a Dictionary’s Keys and Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> for name, age in d.items():

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Looping over a Dictionary’s Keys and Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> for name, age in d.items():

items() gives us key, value pairs

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Looping over a Dictionary’s Keys and Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> for name, age in d.items(): ... print(name, ‘is’, age, ‘years old.’)

items() gives us key, value pairs

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Looping over a Dictionary’s Keys and Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> for name, age in d.items(): ... print(name, ‘is’, age, ‘years old.’) Ayca is 34 years old. Nick is 28 years old. Ondrej is 30 years old. Chris is 29 years old.

items() gives us key, value pairs

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Looping over a Dictionary’s Keys and Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> for name, age in d.items(): ... print(name, ‘is’, age, ‘years old.’) Ayca is 34 years old. Nick is 28 years old. Ondrej is 30 years old. Chris is 29 years old.

print() will automatically concatenate args separated by commas!

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Printing with sep=

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> for name, age in d.items(): ... print(name, age, sep=‘: ’)

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Printing with sep=

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> for name, age in d.items(): ... print(name, age, sep=‘: ’)

sep is an optional argument like end!

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Printing with sep=

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> for name, age in d.items(): ... print(name, age, sep=‘: ’) Ayca: 34 Nick: 28 Ondrej: 30 Chris: 29

sep is an optional argument like end!

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Printing with sep=

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> for name, age in d.items(): ... print(name, age, sep=‘: ’) Ayca: 34 Nick: 28 Ondrej: 30 Chris: 29

the separating string will be printed between the arguments you pass into print()

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Printing with sep=

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> for name, age in d.items(): ... print(name, age, sep=‘: ’) Ayca: 34 Nick: 28 Ondrej: 30 Chris: 29

the default is sep=‘ ’ (insert space)

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Getting a Sorted List of Keys

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’}

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Getting a Sorted List of Keys

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> sorted(d.keys())

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Getting a Sorted List of Keys

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> sorted(d.keys()) [‘Ayca’, ‘Chris’, ‘Nick’, ‘Ondrej’]

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Getting a Sorted List of Keys

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> sorted(d.keys()) [‘Ayca’, ‘Chris’, ‘Nick’, ‘Ondrej’]

sorted() returns a list in alphabetical order!

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Getting a Sorted List of Keys

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> sorted(d.keys()) [‘Ayca’, ‘Chris’, ‘Nick’, ‘Ondrej’] >>> d

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Getting a Sorted List of Keys

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> sorted(d.keys()) [‘Ayca’, ‘Chris’, ‘Nick’, ‘Ondrej’] >>> d [‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’]

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Sorting a Dictionary’s Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’}

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Sorting a Dictionary’s Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> sorted(d.values())

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Sorting a Dictionary’s Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> sorted(d.values()) [28, 29, 30, 34]

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Sorting a Dictionary’s Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> sorted(d.values()) [28, 29, 30, 34]

sorted() returns a list in numerical order!

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Retrieving Min/Max Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’}

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Retrieving Min/Max Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> min(d.values())

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Retrieving Min/Max Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> min(d.values())

returns the smallest element!

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Retrieving Min/Max Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> min(d.values()) 28

returns the smallest element!

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Retrieving Min/Max Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> min(d.values()) 28 >>> max(d.values())

returns the smallest element!

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Retrieving Min/Max Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> min(d.values()) 28 >>> max(d.values())

returns the smallest element! returns the biggest element!

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Retrieving Min/Max Values

>> d = {‘Ayca’: 34, ‘Nick’: 28, ‘Ondrej’: 30, ‘Chris’= 29’} >>> min(d.values()) 28 >>> max(d.values()) 34

returns the smallest element! returns the biggest element!

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What’s next?

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Think/Share:

Implement a phone book using dictionaries

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Nested Data Structures

  • We can nest data structures!

○ Lists in lists ■ grid/game board ○ Lists in dicts ■ animals to feeding times ○ Dicts in dicts ■ your phone’s contact book ○ ... and so on!

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Think/Share:

Make a dictionary of habitat animals and the number of times each animal has been fed.

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Animal – Feedings Dictionary

dict ‘hansa’ ‘kandula’ ‘lumpy’ ‘surus’ 3 2 1 4 keys values

  • animal name ⟶

number of feedings

  • string ⟶ int
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Recall: Animal – Feedings Dictionary

dict ‘hansa’ ‘kandula’ ‘lumpy’ ‘surus’ 3 2 1 4 keys values

  • animal name ⟶

number of feedings

  • string ⟶ int

What if we wanted to store the times that the animals were fed?

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Attempt #1: Animal – Feeding Times Dictionary

dict ‘hansa’ ‘kandula’ ‘lumpy’ ‘surus’

‘12:00,3:00,9:00’ ‘8:00,1:00’ ‘11:00’ ‘5:00,3:00,9:00,2:00’

keys values

  • animal name ⟶

feeding times

  • string ⟶ string

What if we wanted to store the times that the animals were fed?

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Attempt #1: Animal – Feeding Times Dictionary

dict ‘hansa’ ‘kandula’ ‘lumpy’ ‘surus’

‘12:00,3:00,9:00’ ‘8:00,1:00’ ‘11:00’ ‘5:00,3:00,9:00,2:00’

keys values

  • animal name ⟶

feeding times

  • string ⟶ string

Times are not easily accessible!

What if we wanted to store the times that the animals were fed?

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Attempt #1: Animal – Feeding Times Dictionary

dict ‘hansa’ ‘kandula’ ‘lumpy’ ‘surus’

‘12:00,3:00,9:00’ ‘8:00,1:00’ ‘11:00’ ‘5:00,3:00,9:00,2:00’

keys values

  • animal name ⟶

feeding times

  • string ⟶ string

But those times look like a data type we know of......

What if we wanted to store the times that the animals were fed?

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Attempt #2: Animal – Feeding Times Dictionary

dict ‘hansa’ ‘kandula’ ‘lumpy’ ‘surus’

[‘12:00’,‘3:00’,‘9:00’] [‘8:00’,‘1:00’] [‘11:00’] [‘5:00’,‘3:00’,‘9:00’,‘2:00’]

keys values

  • animal name ⟶

feeding times

  • string ⟶ list[string]

What if we wanted to store the times that the animals were fed?