1. Introduction to Computational Thinking
BlockPy
Lists & Iteration
(C) Dennis Kafura

2. Recall: Lists in BlockPy
A list is a data structure that represents an abstraction with multiple instances
Simple lists have instances with only one property
A list represents a “big data” data set
Writing a list “by hand”
“Big Data” list block
(C) Dennis Kafura

3. Recall: Iteration in BlockPy
BlockPy has blocks for iteration
Use iteration to process a data set (i.e., a list)
Different patterns for processing a data set
Uniform
Accumulate
Transform
Filter
List Property
Iteration Property
Iteration
Actions go here
Singular and plural
(C) Dennis Kafura

4. Patterns
Uniform: perform the same processing on each element of the list
Accumulate: determine a property of the list
Transform: produce a new list by processing the elements of an existing list
Filter: use a decision to select some elements of the list for processing
(C) Dennis Kafura

5. Transform pattern
Motivation: generate a “transformation” of the abstraction being processed
Create a list of forecast temperatures in Celsius from a list of temperatures in Fahrenheit.
Create a list of “feels like” temperatures from a list of weather forecasts that give temperature and wind speed.
Create a list that categorizes each state’s crime rate as high, medium, or low from a list of crime rates by state. 4 14 9 2 15 7 10
How do we go from here…
To this? 8 28 18 4 30 14 20
(C) Dennis Kafura

6. Transform pattern Creates a new list based on an existing list
Uses list operations
create an empty list
append (“add”) a new item to end of a list
Before Iteration
During Iteration
(C) Dennis Kafura

7. Transform pattern iteration Existing List A Process: A -> B
New List B
append
(C) Dennis Kafura

8. Transform in action List Property representing an Abstraction
Property representing a New List
Iteration
Put stuff into our New List Property
*Vocab: “Append” means “Add to end”
(C) Dennis Kafura

9. Plotting Making lists means making plots!
A list of numbers (over time)
Two equal-sized lists of numbers
Any list of numbers
Actually draw the plot
Awesome people give titles
(C) Dennis Kafura

10. Plot, then Show
After you plot…
YOU MUST SHOW
(C) Dennis Kafura

11. Print vs Plotting Printing is for Quantitative Measures
Plotting is for lists
(C) Dennis Kafura

12. Filter pattern
Motivation: in big data only certain occurrences may be of interest
Big earthquakes
Temperatures above or below a certain threshold
A high or low crime rate
Mechanism: combine
iteration – to provide each element one at a time
decision – use each element that passes the filter test and ignore others
(C) Dennis Kafura

13. Filter pattern iteration Existing List A If filter test for A is false
true A
append
New List
(C) Dennis Kafura

14. Filtering in BlockPy
Iteration
Decision
Append
(C) Dennis Kafura

15. Next steps today
Work on the assigned BlockPy and list problems in the book using iteration and decision
Work as an individual
Seek help from and provide help to your cohort
Go as far and as fast as you can remembering to keep everyone in your cohort on board
Cohort feedback/reports
(C) Dennis Kafura