NETLOGO LISTS

1. NETLOGO LISTS Or… James says, “fput THIS!”

2. What are LISTS? • Shopping list • Address list • DNA sequences • Any collection of similar or dissimilar things • Often are ordered in some way

3. What are LISTS? • A list is a variable that contains a list of values. • Lists can contain any type of value, including other lists. • Lists can contain different types of values at once.

4. Examples of NetLogo Lists • [ ] • [ 1 2 3 99 -2.9 ] • [ “a” “sam” ] • [ [ -1 0 ] [ 1 1 ] [ 1 -1 ] ] • [ “g” “a” “c” “t” ] • [ 12 “bob” [ 3 12 4 ] ]

5. List Syntax • Zero or more values surrounded by square brackets [ ] • Values are separated by “white space” • Values are NOT separated by commas, or any other punctuation!

6. GOOD [ ] [ 1 2 3 ] [ “Hello!” “I am James!” ] BAD [ 1, 2, 3, 4 ] 5 4 6 { “A” “B” “C” } Good and Bad Syntax Examples

7. Creating Lists • Three ways to create lists • Assign the empty list • Assign a list of constants • Assign the results of list constructors

8. The Empty List – [ ] • Assigning [ ] to a variable makes it an empty list. ; erase turtle’s memory set memory [ ] ; memory is now an empty list (likewise, “” creates an empty string)

9. Lists of Constants – Part 1 set friends [ “Bob” 25 “Mary” 41 ] set my-rgb [ .5 .75 .1 ] set dna [ “c” “t” “a” “g” “a” “g” “t” “t” ]

10. Lists of Constants – Part 2 • Lists of Lists of constants • set successes [ [ 7 “B”] [ 8 7 “Z” ] [ 3 ] ] • set matrix [ [ 1 0 0 ] [ 0 1 0 ] [ 0 0 1 ] ]

11. Lists of Constants – Part 3 • For some reason, this only works with constants, not variables. • So, this will not work: set my-list [ heading xcor ycor ] Fortunately, there is a way to build lists with variables.

12. List Constructors • There are many primitive reporters that report a list. • Some create a list from other things. • Some take a list as input, and can be used to modify lists.

13. but-first but-last filter fput list lput map modes n-values remove remove-duplicates remove-item replace-item reverse sentence shuffle sort, sort-by values-from List Constructor Primitives

14. Two Words About Strings • Lists and Strings share some primitives. …however… • A string is not a list of characters. • String: “bob” • List: [ “b” “o” “b” ]

15. List – The Fresh List Maker • Syntax: list {item1} {item2} • reports a list containing the two inputs • print list thing other-thing • O> [ -2 5 ] • Print list (xcor * 2) color • T> [ 10.0 9.9999 ]

16. List – Code-Fu • Wrap list and the items in ( ) to create lists with any number of items at once. • print (list xcor heading label) • T> [ -2.0 322.43 “walrus” ] • print (list population) ; one item • O> [ 10000 ] • print (list ) ; zero items • O> [ ]

17. Values-From – Agent Sucker • values-from {agentset} [ {reporter} ] • makes a list of values calculated by an agentset print values-from turtles [ heading ] O> [ 45 90 135 ]

18. Values-From • used often for aggregating agent data print sum values-from turtles [ net-worth ] print mean values-from neighbors [ age ] • used to load an agentset into a list set patch-list values-from patches [ self ]

19. fput – lput • lput {value} {list} ; (last) • fput {value} {list} ; (first) • use to build up lists one item at a time • reports a list that is the given list with the value appended, becoming the new last or first item. ; add this taste to memory list set memory lput taste memory

20. but-first – but-last • but-first {list} but-last {list} • reports the result of removing the first or last item from the given list • print but-first [ “bird” “cat” “dog” ] O> [ “cat” “dog” ]

21. Combining fput & but-last • Combine these to update a “constant-length” list • ; add new memory, forget oldest memory set memory fput taste ( but-last memory ) • Likewise, lput and but-first • set queue but-first (lput customer queue)

22. Item – the List Interrogator • item {index} {list} • items in a list are indexed by number • the first list item has an index of zero • the “item” primitive returns the value of an item in a list at the given index • set info [ “a” “b” “huh?” “bob” ] print item 2 info O> huh?

23. REMEMBER! • List-making primitives are reporters! • Primitives that “modify” a list don’t actually change the input list, but report a result based on the list. • So, to modify a list, the result must be assigned back to the input list.

24. Using Lists - Length • Length reports the number of items in the list. • Watch out for using Count when you want to use Length! • count is for agentsets • length is for lists (and strings)

25. Using Lists – First, Last • Shorthand to get the first or last elements of a list • First returns the first list item. • ( first my-list ) same as (item 0 my-list ) • Last returns the last item • ( last my-list ) same as ( item ( ( length my-list ) - 1 ) my-list

26. Basic List Tools • Reverse • Reverses the order of the items in the list • Sort • Sorts the list • Shuffle • Randomizes the list

27. LISTS Code-Fu • These list primitives are powerful tools for manipulating lists. • They are the amateur programmer’s friend. (pro programmers, too) • They let us easily Convert, Combine, Reduce, Analyze, Fold, Spindle, and Mutilate lists • Without these, you’d need to write some rather complicated code to achieve the same results

28. LISTS Code-Fu - MAP • map [ {reporter} ] {list} • ( map [ {reporter} ] {list1} {list2} {…} ) • Map lets us perform the same operation on every item of a list, creating a new list with the results

29. LISTS Code-Fu - MAP • Double the value of each item in the list • The following two slides show how to perform a simple task on every item in a list • Both sets of code use the following assumptions: • (which you don’t need to memorize…this is only FYI) • the variable original-list exists • the variable index exists • the variable modified-list exists

30. LISTS Code-Fu - MAP • Double the value of each item in the list • The “hard” way, without map set original-list [ 1 2 3 4 ] set index 0 set modified-list [ ] repeat ( length original-list ) [ set modified-list (lput((item index original-list)* 2)) set index index + 1 ] print original-list + “ x 2 = “ + modified-list O> [ 1 2 3 4 ] x 2 = [ 2 4 6 8 ]

31. LISTS Code-Fu - MAP • Double the value of each item in the list • The “easy” way, with map set original-list [ 1 2 3 4 ] set modified-list map [ ? * 2 ] original-list print original-list + “ x 2 = “ + modified-list O> [ 1 2 3 4 ] x 2 = [ 2 4 6 8 ]

32. LISTS Code-Fu - MAP • Add two lists, making a third list • set income [ 100 101 54 242 ] set outgo [ 123 99 75 99 ] set net-worth ( map [ ?1 - ?2 ] income outgo )

33. Things to look at more: • Filter • Creates a list by selecting the items in the given list that match the criteria • Reduce • Reduces a list to a single value, using the formula you specify • Foreach • Like MAP, but lets you run code on the list items, rather than making a new list

34. Turtle or Patch Memory Choices made Patches visited State history Group members Arrays of properties DNA, “Genes” Preset information Plot data Lines read from files Undo history Route history Queues Stacks Matrices You Name It! LIST Ideas