1. Lists
Alice

2. Collections
In some animations, several objects must perform the same actions
Example:
A marching band, where the band members are performing the same marching steps.
In such situations, it is convenient to collect all the objects into a group (a collection)

3. List One way to organize objects into a collection is to use a list.
In our daily lives, we use lists to help us organize things. For example,
assignments list
shopping list
In programming, a list is known as a data structure.

4. Types of Lists
In Alice, a list can be a list of numbers or a list of objects, colors, or other type ….
In this session, we will use an example of a list of objects.

5. Example
The famous Rockettes® are preparing for their winter holiday show. You have been hired to create an animation for the holiday show that will be used on a web site where people can purchase tickets for the show.

6. Creating a list: Step 1
Create the initial world and add five rockette objects to the world.
Then, create a new world-level variable in the properties panel.
(Why should it be world-level rather than class-level?)

7. Creating a list: Step 2 In the popup dialog box, type in a name
select Object type
check “make a List” box
click new item button 5
times to select each
of the 5 rockettes,
one at a time

8. Programming with a list
Now that a list has been created, how do we use the list in a program?
One of the most useful operations with a list is to repeatedly perform some action with each item in the list. We call this iteration or "iterating through a list."

9. Iterating through a list
Iteration can be done in two ways:
in order (one at a time)
all together (simultaneously)

10. Example: Iteration in Order
A typical chorus line dance involves each dancer (one after the other) kicking up one leg.
Possible storyboard:
kickUpRightLeg
Parameter: whichRockette
Do in order
Do together
whichRockette right thigh turn back
whichRockette right calf turn forward
whichRockette right calf turn back
For all dancers in order
item_from_dancers kickUpRightLeg

11. Demo Ch09Lec1Rockette-V1 Concepts illustrated in this example
A method that defines an action to be performed by objects in a list is a world-level method (it involves more than one object).
In this example, kickUpRightLeg
The For all in order statement traverses the list, one list item at a time.

12. Demo Ch09Lec1Rockettes-V2 Concepts
The For all together statement executes the action for all list items simultaneously.
The kickUpRightLeg method is still the same. All we did was call the method from within a For all together iterative loop.

13. Assignment
Read Chapter 9 Section 1, Lists

14. Lab
Chapter 9 Lecture 1 Lab