hi here are the collection extensions we use in Moose. I copied them to PharoTaskForces so that we can discuss and tweak the code if wanted. My favorite is flatCollect:/flatCollectAsSet: groupedBy: There are really useful. Stef testFlatCollectArray "self debug: #testFlatCollectArray" self assert: ((#((1 2) (3 4) (5 3)) flatCollect: [ :each ]) = #(1 2 3 4 5 3)). self assert: ((#((1 2) (2 3) (1 3 4)) flatCollect: [:each]) = #(1 2 2 3 1 3 4)). self assert: ((#((1 2) (2 3) () ()) flatCollect: [:each]) = #(1 2 2 3)). self assert: ((#((1 2) (2 3) (1 3 4)) flatCollect: [:each| Array with: each]) = #(#(1 2) #(2 3) #(1 3 4))). self assert: ((#((1 2) (2 3) (1 3 4)) flatCollect: [:each| Set with: each]) = #(#(1 2) #(2 3) #(1 3 4))). testFlatCollectSet "self debug: #testFlatCollectSet" self assert: ((#((1 2) (1 2) (1 3 4)) asSet flatCollect: [:each]) = #(1 1 2 3 4) asSet). self assert: ((#() asSet flatCollect: [:each]) = #() asSet). self assert: ((#((1 2) () (1 3 4)) asSet flatCollect: [:each]) = #(1 1 2 3 4) asSet). self assert: ((#((1 2) #((99)) (1 3 4)) asSet flatCollect: [:each]) = #(1 1 2 3 4 (99)) asSet). self assert: ((#((1 2) #(()) (1 3 4)) asSet flatCollect: [:each]) = #(1 1 2 3 4 ()) asSet). testCollectAsSet "self debug: #testCollectAsSet" self assert: ((#() collectAsSet: [:each | each odd]) = Set new). self assert: (#(1 2 3 4 5 6) collectAsSet: [:each | each odd]) = (Set with: true with: false). self assert: (#(1 3 5 7 9 11) collectAsSet: [:each | each odd]) = (Set with: true). self assert: (#(1 2 3 4 5 4 3 2 1) collectAsSet: [:each | each]) = (1 to: 5) asSet. testGroupedByArray "self debug: #testGroupedByArray" | res | res := #(1 2 3 4 5) groupedBy: [:each | each odd]. self assert: (res at: true) = #(1 3 5). self assert: (res at: false) = #(2 4) Set>>flatCollect: aBlock ^self flatCollectAsSet: aBlock Symbol>>value "Allow this object to act as a ValueHolder on itself." ^self OrderedCollection>>removeAtIndex: anIndex "Remove the element of the collection at position anIndex. Answer the object removed." | obj | obj := self at: anIndex. self removeIndex: anIndex + firstIndex - 1. ^obj Collection ============================== collectAsSet: aBlock "Evaluates aBlock for each element of the receiver and collects the resulting values into a Set." "This is an efficient shorthand for [ (self collect: aBlock) asSet ]." "originally developed by a. kuhn and released under MIT." ^self inject: Set new into: [ :set :each | set add: (aBlock value: each); yourself ]. copyEmpty: aSize "Answer a copy of the receiver that contains no elements. This method should be redefined in subclasses that add instance variables, so that the state of those variables is preserved" ^self class new: aSize flatCollect: aBlock "Evaluate aBlock for each of the receiver's elements and answer the list of all resulting values flatten one level. Assumes that aBlock returns some kind of collection for each element. Equivalent to the lisp's mapcan" "original written by a. Kuhn and released under MIT" | stream | self isEmpty ifTrue: [ ^ self copy ]. stream := (self species new: 0) nsWriteStream. self do: [ :each | stream nextPutAll: (aBlock value: each) ]. ^ stream contents flatCollectAsSet: aBlock "Evaluate aBlock for each of the receiver's elements and answer the list of all resulting values flatten one level. Assumes that aBlock returns some kind of collection for each element. Equivalent to the lisp's mapcan" "original written by a. Kuhn and released under MIT" | set | self isEmpty ifTrue: [^self copy ]. set := Set new. self do: [ :each | set addAll: (aBlock value: each) ]. ^set flatten "Recursively collect each non-collection element of the receiver and its descendant collections. Please note, this implementation assumes that strings are to be treated as objects rather than as collection." ^self gather: [ :each ] groupedBy: aBlock "Return a dictionary whose keys are the result of evaluating aBlock for all elements in the collection, and the value for each key is the collection of elements that evaluated to that key. e.g. #(1 2 3 4 5) groupedBy: [:each | each odd] a Dictionary true ---> #( 1 3 5) false --> #(2 4) originally developed by a. kuhn and released under MIT." | result | result := Dictionary new. self do: [:each | | key collection | key := aBlock value: each. collection := result at: key ifAbsentPut: [OrderedCollection new]. collection add: each]. self species ~~ OrderedCollection ifTrue: ["Convert the result collections to be the right type. Note that it should be safe to modify the dictionary while iterating because we only replace values for existing keys" result keysAndValuesDo: [:key :value | result at: key put: (self species withAll: value)]]. ^result includesAll: aCollection "Answer true if the receiver includes all elements of aCollection with at least as many occurrences as in aCollection. For a less strict comparison please refer to supersetOf: and its inverse subsetOf:." ^(aCollection isCollection) and: [ aCollection size <= self size and: [ aCollection allSatisfy: [ :each | (aCollection occurrencesOf: each) <= (self occurrencesOf: each) ]]] nilSafeGroupedBy: aBlock ^ self groupedBy: [ :each | | value | value := aBlock value: each. value ifNil: [ UndefinedObject ]. ] selectAsSet: aBlock "Evaluate aBlock with each of the receiver's elements as the argument. Collect into a new set, only those elements for which aBlock evaluates to true. Answer the new collection." | newSet | newSet := Set new. self do: [:each | (aBlock value: each) ifTrue: [newSet add: each]]. ^newSet shuffle "Swaps the receiver's elements at random." self shuffle: (self size * self size log) asInteger sum: aSymbolOrBlock ^self inject: 0 into: [:sum :each | sum + (aSymbolOrBlock value: each)] shuffle: times "Swaps random elements of the receiver." | size random | size := self size. random := Random new. times timesRepeat: [ self swap: (random next * size) floor + 1 with: (random next * size) floor + 1 ].