1. Introduction to Computational Thinking
Abstraction &
Data Structures
(C) Dennis Kafura 2016

2. Abstraction & Data Structures
identifying the information properties of an entity relevant for a given stakeholder; each property has a value.
computer
property --> value
abstraction
property --> value
data structure
state
property --> value
algorithm
organizing the properties and their values so that they can be processed by an algorithm executed by a computer.
(C) Dennis Kafura 2016

3. Abstraction An abstraction can be depicted by a table
Example: an abstraction of a weather report
properties
City
Temperature
“Blacksburg, VA” 77
values
(C) Dennis Kafura 2016

4. Dictionary: a data structure
A dictionary is a data structure used to represent a single instance
A dictionary is organized as a collection of property-value pairs
In Python the term key-value pair is used
City
Temperature
“Blacksburg, VA” 77
key-value pair
key-value pair
temps = { “City” : “Blacksburg, VA”, “Temperature” : 77}
key
value
(C) Dennis Kafura 2016

5. Dictionary operations
temps = { “ City” :“Blacksburg, VA” , “Temperature” : 77}
retrieval
cityTemp = temps[“Temperature”]
cityName = temps[“City”]
update
temps[“Temperature”] = 82
(C) Dennis Kafura 2016

6. For today
Work in your cohorts on the class work problems for 30 minutes
More discussion of abstraction and dictionaries to follow
(C) Dennis Kafura 2016

7. Abstracting multiple entities
Similar abstracted entities (e.g., weather reports for different locations) have the same properties but different values.
They are called instances.
properties
City
Temperature
“Blacksburg, VA” 77
“New York, NY” 85
“San Jose, CA” 75
“Miami, FL” 88
instances
(C) Dennis Kafura 2016

8. Representing an abstraction
City
Temperature
“Blacksburg, VA” 77
“New York, NY” 85
“San Jose, CA” 75
“Miami, FL” 88
list
multiple instances,
one property
dictionary
multiple properties
one instance
(C) Dennis Kafura 2016

9. Representing Abstractions
Abstractions are represented using data structures
Dictionary
a collection of key-value pairs
used to represent multiple properties of a single instance of an abstraction
List
a collection of similar things
used to represent one property of multiple instances of an abstraction
(C) Dennis Kafura 2016

10. An Example City Temperature “Blacksburg, VA” 77 “New York, NY” 85
“San Jose, CA” 75
“Miami, FL” 88
report =
[ { “ City” : “Blacksburg, VA” , “Temperature” : 77} ,
{ “ City” : “New York, NY” , “Temperature” : 85} ,
{ “ City” : “San Jose, CA” , “Temperature” : 75} ,
{ “ City” : “Miami, FL” , “Temperature” : 88} ]
(C) Dennis Kafura 2016

11. Dictionaries/Lists and iteration
reports =
[ { “ City” : “Blacksburg, VA” , “Temperature” : 77} ,
{ “ City” : “New York, NY” , “Temperature” : 85} ,
{ “ City” : “San Jose, CA” , “Temperature” : 75} ,
{ “ City” : “Miami, FL” , “Temperature” : 88} ]
# find average temperature
total = 0
number= 0
for report in reports:
total= total + report[“Temperature”]
number = number + 1
average = total / number
(C) Dennis Kafura 2016