This document provides an overview of Groovy's collection API. It discusses how Groovy treats many objects like collections, including strings, numbers, and regular expressions. It demonstrates various collection notation and operations, including lists, maps, ranges, and spread operators. It also summarizes common collection methods like each, find, collect, reducers, and useful utility methods like groupBy, countBy, and set operations.

1. Groovy Collection API
Trygve Amundsen, Kodemaker

2. basics

3. groovy collections
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•
•
•
•
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Java Collection (List, Map, Set mfl.)
Array
String
Regexp
Iterable
CharSequence
Object!
assert "string".collect { it } == ['s','t','r','i','n','g']
assert 42.collect { it } == [42]
// string

4. notation, lists
def emptyList = []
assert [] instanceof ArrayList
def list = [1,2,3]
assert list[1..-1] == [2,3]
assert list[-3..-2] == [1,2]
assert list[2..1] == [3,2]

5. notation, maps
def emptyMap = [:]
assert [:] instanceof LinkedHashMap // predictable order
assert [a:1, b:2] == ['a':1, 'b':2]
method(a:1, b:2)
// illusion of named parameters

6. ranges are lists
assert (1..3) == [1,2,3]
assert (1..<3) == [1,2]
assert (1..3) instanceof IntRange // groovy.lang
assert (1..3) instanceof List

7. notation, list operators
assert
assert
assert
assert
[1,2] << 3 == [1,2,3]
// leftShift()
[1,2]+3 == [1,2,3]
// plus()
[1,2]+[3,4] == [1,2,3,4]
[1,2,3]-[3,4] == [1,2]
// minus()

8. notation, spread operator
assert ["a","b","1"]*.isNumber() == [false,false,true]
assert ["a","b","1"].number == [false,false,true]

9. basics, api

10. each
[1,2,3].each { println it}
[1,2,3].each { item -> println item }
[1,2,3].eachWithIndex { item, i -> println "index ${i} contains ${item}" }
[1,2,3].reverseEach { println it }

11. find (filters)
assert [1,2,3].findAll { it % 2 } == [1,3]
assert [1,2,3].find { it % 2 } == 1
assert [1,2,3].findIndexValues { it %2 } == [0,2]

12. collect (map)
assert [1,2,3].collect { it * it } == [1,4,9]
assert [1,[2,3],4].collectNested { it*it } == [1,[4,9],16]
assert [1,2,3].collectEntries { ['k' +it, it] } == [k1:1,k2:2,k3:3]

13. method returns
item content
collect
collectEntries
collectNested
Object
sort
groupBy
findAll
unique
tail
drop/take
stack
push/pop
max, min, sum, count
join
inject
Collection
multiple items
one item
each
eachWithIndex
reverseEach
find
head
first/last
changed
countBy
findResults
collectMany
split
plus
minus
intersect
subsequences
permutations
combinations
set
boolean
unchanged
changed
number of items
unchanged
any
every

14. reducers
assert [1,2,3].max() == 3
assert [1,2,3].min() == 1
assert [1,2,3].sum() == 6
assert [1,2,3].max{ -it } == 1
assert [1,2,3].max{ a,b-> b<=>a } == 1

15. reducers, cont’d
assert [1,2,3].any{ it > 3 } == false
assert [1,2,3].every{ it < 4 } == true
assert [1,2,3].join(";") == "1;2;3"

16. reducers, inject
assert [1,2,3].inject(0)
{ acc, val -> acc+val } == 6
assert [1,2,3].inject("0") { acc, val -> acc+val } == "0123"
assert [1,2,3].inject([]) { acc, val -> acc+val } == [1,2,3]
assert [a:1,b:2].inject(0) { acc, key, val -> acc+val } == 3

17. inject -> reduce
Object.metaClass.reduce = {initial, closure->
delegate.inject(initial, closure)
}
[1,2,3].reduce(0){acc,val->acc+val}

18. useful methods

19. groupBy, countBy
assert [1,2,3].groupBy{it < 2 ? 'small' : 'big'} == [small:[1], big:[2,3]]
assert [1,2,3].countBy{it < 2 ? 'small' : 'big'} == [small:1,
big:2]

20. set operations
assert [1,2]+3 == [1,2,3]
assert [1,2]+[3,4] == [1,2,3,4]
assert [1,2].plus([3,4]) == [1,2,3,4]
assert [1,2,3]-3 == [1,2]
assert [1,2,3]-[2,3] == [1]
assert [1,2,3].minus([2,3]) == [1]
assert [1,2,3].intersect([3,4]) == [3]
assert [1,2,3].disjoint([4,5]) == true
assert [1,2,3].subsequences() == [[3], [1, 2, 3], [1], [2], [2, 3], [1, 3], [1, 2]] as Set
assert [1,2,3].permutations() == [[1, 2, 3], [2, 3, 1], [3, 2, 1], [3, 1, 2], [2, 1, 3], [1, 3, 2]] as Set
assert [[1,2],[3,4]].combinations() == [[1, 3], [2, 3], [1, 4], [2, 4]]

21. Nested Collections
assert [1,[2,3],4].flatten() == [1,2,3,4]
assert [1,[2,3],4].collectNested { it+10 } == [11,[12,13],14]
assert [['a','b'], [1,2]].transpose() == [['a',1],['b',2]]

22. functional style
assert [1,2,3].head() == 1
assert [1,2,3].tail() == [2,3]
assert [1,2,3].first() == 1
assert [1,2,3].last() == 3
assert [1,2,3].take(2) == [1,2]
assert [1,2,3].drop(2) == [3]
assert [1,2,3].split { it<3 } == [[1,2],[3]]

23. list as stack
NOTE: mutates!
def list = [1,2,3]
list.push(4)
assert list == [1,2,3,4]
assert list.pop() == 4
assert list == [1,2,3]

24. findResults
assert [1,2,3].findResults { it > 1 ? it*it : null } == [4,9]
[1,2,3].findResults { it > 1 ? it*it : null }
is identical to
[1,2,3].findAll { it > 1 }
.collect { it*it }

25. Other, possibly useful methods
assert [1,2,3].collectMany { [it**2, it**3] } == [1,1,4,8,9,27]

26. map withDefault
def newMap = [:].withDefault { [] }
[a:1,b:2,c:2].each { key, val ->
newMap[val] << key
}
assert newMap == [1:['a'], 2:['b','c']]

27. mutability
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all methods return new collections/objects
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a few exceptions exist, such as push/pop and sort(boolean mutate)
objects and collections are generally mutable
use asImmutable(), asSynchronized() for multithreading
or better: use gpars (included in groovy jdk)
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(that’s a different talk - coming up on groovy meetup!)

28. doc & src

29. Groovy JDK doc

30. Groovy JDK doc

31. DefaultGroovyMethods

32. real-world example
params.findAll { key, val ->
// filtrer kun diagnose-parametre
key.startsWith(paramPrefix+"diagnoser")
}.groupBy { key, val ->
// grupper på rader
key.substring(0,"diagnoser[0]".size())
}.findAll { rowKey, rowMap ->
// Fjern tomme rader
rowMap.any { key, val -> val && val != "null" }
}.inject([:]) { acc, key, val ->
// ungroup rader (tilbake til en map med parametre)
acc + val
}.collectEntries { key, val ->
// hent sykdomskode.id
if (key.endsWith('.sykdomskode') && val) {
[key+'.id', Sykdomskode.findByNr(val)?.id ?: ""]
} else {
[key, val]
}
}.sort {
it.key
}

33. more...
groovy.codehaus.org
meetup.com/Oslo-Groovy-Meetup

34. questions ?

35. Ubrukt

36. sample data
@EqualsAndHashCode @ToString class Person { def name, address, pets }
@EqualsAndHashCode @ToString class Address { def street, city }
enum Pet { CAT, DOG, BIRD, DUCK }
import static Pet.*
def persons = [
new Person(name:"Ole",
address:new Address(street:"Blindvn 1", city:"Oslo"),
pets:[BIRD, CAT]),
new Person(name:"Dole",
address:new Address(street:"Blindvn 2", city:"Oslo"),
pets:[DOG, CAT]),
new Person(name:"Doff",
address:new Address(street:"Strandvn 9", city:"Bergen"),
pets:[BIRD, DOG]),
]
assert persons.pets == [ [BIRD, CAT], [DOG, CAT], [BIRD, DOG]]
assert persons.pets.flatten().unique() == [BIRD, CAT, DOG]
assert persons.address.city.unique() == ["Oslo", "Bergen"]

37. real-world example
import org.ccil.cowan.tagsoup.Parser
@Grab(group='org.ccil.cowan.tagsoup', module='tagsoup', version='0.9.7')
def gdocHome = "http://groovy.codehaus.org/groovy-jdk/"
def gdocs = ["java/lang": ["Object[]","Object"],
"java/util": ["Collection", "List", "Map"]]
gdocs.inject([:]) { agg, key, val ->
// create map of [class:url]
agg + val.collectEntries { [it, gdocHome + key+"/"+it+".html" ] }
}.collectEntries { className, url ->
// parse urls
def html = new XmlParser(new Parser()).parse(url)
[className, html.body.table[1].tr[1..-1].collect {
it.td[1].code.b.a.text()
}]
}

38. • gå dypt i utvalgte kall, ex
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groupBy
inject
findResult: find + transform
nested collections: collectNested

39. Groovy Collection Jdk Doc
• Object
• Object[]
• Collection
• Map
• List
• Set

40. Basic collection types
assert
assert
assert
assert
assert
[] instanceof ArrayList
// (java.util)
[:] instanceof LinkedHashMap
// predictable order
([] as Set) instanceof HashSet
(1..3) instanceof IntRange
// groovy.lang
(1..3) instanceof List