11. Data Structures in Smalltalk

• Pre-Defined Data Structures in Smalltalk
• Collections hierarchy
• Operations on collections
• -Functional Programming
• Differences between kinds of collections
• Collections Hierarchy
• 
• Operations on Collections
• They all understand
• -size
• -adding new elements (add:, addAll:, with:with:)
• -removing new elements (remove:, remove:ifAbsent:)
• -testing for elements (includes:, isEmpty, occurencesOf:)
• -enumerating elements (do:, select:, reject:, collect:, detect:)
• Demonstrating do:
• | aString |
• aString := 'Now is the time for all good men to come to the aid of their blah blah blah'.
• count := 0.
• aString do: [:letter | letter asLowercase == $a ifTrue: [count := count + 1.]] .
• count "--> 5"
• Differences between select:, reject:, and detect:
• | aString |
• aString := 'Now is the time for all good men to come to the aid of their blah blah blah'.
• aString select: [:each | each isVowel].
• " --> 'oieieoaooeooeoeaioeiaaa' "

• ---

• aString reject: [:gobbledy | gobbledy isVowel].
• " --> 'Nw s th tm fr ll gd mn t cm t th d f thr blh blh blh'"

• ---

• aString detect: [:gobbledy | gobbledy isVowel].
• " --> $o"
• What collect: and inject: do
• | someNumbers |
• someNumbers := #(1 2 3 4 5 6 7).
• someNumbers collect: [:aNumber | aNumber + 1].
• "--> (2 3 4 5 6 7 8 )"

• ---

• someNumbers inject: 0 into: [:subTotal :nextNumber | subTotal + nextNumber].
• "--> 28"
• Other ways to use inject: (functional programming)
• | aString |
• aString := 'Now is the time for all good men to come to the aid of their blah blah blah'.
• aString inject: 0
• into: [:count :nextElement |
• count + (nextElement asLowercase == $a ifTrue: [1] ifFalse: [0])]
• "--> 5"
• inject: is actually select: or reject: or...
• | aString |
• aString := 'Now is the time for all good men to come to the aid of their blah blah blah'.
• "inject: as select:"
• aString inject: '' into: [:newString :nextCharacter |
• newString , (nextCharacter isVowel ifTrue: [nextCharacter asString] ifFalse: [''])].
• "--> 'oieieoaooeooeoeaioeiaaa'"
• Side note: Tokenizing
• "First parse into words"
• | aString |
• aString := 'Now is the time for all good men to come to the aid of their blah blah blah'.
• aString findTokens: ' '.
• "--> OrderedCollection ('Now' 'is' 'the' 'time' 'for' 'all' 'good' 'men' 'to' 'come' 'to' 'the' 'aid' 'of' 'their' 'blah' 'blah' 'blah' )"
• Bags vs. Sets
• | aString someWords |
• aString := 'Now is the time for all good men to come to the aid of their blah blah blah'.
• someWords := Bag new.
• (aString findTokens: ' ') do: [:aWord | someWords add: aWord].
• someWords
• "--> Bag ('blah' 'blah' 'blah' 'men' 'of' 'the' 'the' 'aid' 'their' 'all' 'to' 'to' 'time' 'Now' 'for' 'good' 'is' 'come' )"

• ---

• someWords := Set new.
• (aString findTokens: ' ') do: [:aWord | someWords add: aWord].
• someWords
• "--> Set ('blah' 'men' 'of' 'the' 'aid' 'their' 'all' 'to' 'time' 'Now' 'for' 'good' 'is' 'come' )"
• SequenceableCollection New Abilities
• atAll: aCollection put: anObject
• atAll: anObject
• first
• last
• indexOf: anElement
• indexOf: anElement ifAbsent: someBlock
• indexOfSubCollection: aSubCollection startingAt: anIndex
• replaceFrom: start to: stop with: replacementCollection

• ---

• , anotherSequenceableCollection
• copyFrom: start to: stop
• copyReplaceAll: oldSubCollection with: newsubCollection
• copyWith: newelement
• copyWithout: oldelement

• ---

• findFirst: aBlock
• findLast: aBlock
• with: anotherSequenceable do: aBlock
• Examples:
• | aString someWords|
• aString := 'Now is the time for all good men to come to the aid of their blah blah blah'.
• someWords := aString findTokens: ' '.
• someWords indexOf: 'blah'.
• "--> 16"

• ---

• someWords replaceFrom: 1 to: 2 with: #('Then' 'was')
• "--> OrderedCollection ('Then' 'was' 'the' 'time' 'for' 'all' 'good' 'men' 'to' 'come' 'to' 'the' 'aid' 'of' 'their' 'blah' 'blah' 'blah' )"

• ---

• someWords copyReplaceAll: #('Now' 'is') with: #('Then' 'was' 'almost')
• "--> OrderedCollection ('Then' 'was' 'almost' 'the' 'time' 'for' 'all' 'good' 'men' 'to' 'come' 'to' 'the' 'aid' 'of' 'their' 'blah' 'blah' 'blah' )"
• OrderedCollection new methods
• after: oldObject
• before: oldObject
• add: blah after: oldblah
• addFirst:, addLast:
• removeFirst, removeLast
• SortedCollection
• | aString someWords|
• aString := 'Now is the time for all good men to come to the aid of their blah blah blah'.
• someWords := SortedCollection new.
• someWords sortBlock: [:one :two | one <= two].
• (aString findTokens: ' ') do: [:aWord | someWords add: aWord].
• someWords
• "--> SortedCollection ('aid' 'all' 'blah' 'blah' 'blah' 'come' 'for' 'good' 'is' 'men' 'Now' 'of' 'the' 'the' 'their' 'time' 'to' 'to' )"
• LinkedList
• addFirst: aLink, nextLink: aLink, removeFirst, removeLast
• (Like OrderedCollection, but faster.)
• Interval
• (10 to: 100 by: 6) do: [:i | count := count + i].
• Strings and Texts
• Texts are Strings that also have font and style
• Strings can do some cool things
• '#irst string' match: 'first string' "--> true"
• Symbols
• Symbols are strings that are guaranteed to be unique
• (stored in only one place).
• => Very fast lookup. (Don't have to walk the string, just check the location.)
• Symbols are used internally for method name lookup.
• Games with symbols
• Circle exampleOne.

• ---

• Circle perform: #exampleOne.

• ---

• a := #exampleOne.
• Circle perform: a

• ---

• b := Circle.
• a := #exampleOne.
• b perform: a