Kotlin Collection関数をマスター

by LINE Digital Frontier - TECH

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Kotlin Collectionؔ਺ΛϚελʔ 2024.06.22 Masayuki Suda © LINE Digital Frontier Corporation ύϑΥʔϚϯεͱՄಡੑΛཱ྆

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໨࣍ 01. ΠϯτϩμΫγϣϯ 1.1 ࣗݾ঺հ 1.2 ͖͔͚ͬ 04. ؔ਺ͷ঺հ2 4.1 ෦෼औಘ 4.2 ୯Ұཁૉऔಘ 05. ߴ౓ͳؔ਺ͷ࢖༻ྫ 5.1 chunked 5.2 windowed 02. Kotlin Collectionͷ֓ཁ 2.1 ϑϨʔϜϫʔΫجຊߏ଄ 2.2 ओཁͳΠϯλʔϑΣʔε 03. ؔ਺ͷ঺հ1 3.1 ม׵ 3.2 ϑΟϧλϦϯά 06. ύϑΥʔϚϯεͷ࠷దԽ 6.1 Sequenceͱforจ 6.2 ·ͱΊ 3.3 ཁૉͷ௥Ճɾ࡟আ 3.4 άϧʔϓԽ 4.3 ฒ΂ସ͑ 4.4 ू໿ؔ਺

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ΠϯτϩμΫγϣϯ 01. ࣗݾ঺հ ͖͔͚ͬ

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1.1 ࣗݾ঺հ LINE Digital Frontier גࣜձࣾͱ͸

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1.2 ͖͔͚ͬ ɾKotlin Collectionͷ֦ுؔ਺ͬͯ΋ͷ͍͢͝਺͕͋Δ͚Ͳ͋·Γ஌Βͳ͍ ɾશ෦͓͞Β͍͢Δػձ͕͋Δͱخ͍͠ͳ

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Kotlin Collectionͷ֓ཁ ϑϨʔϜϫʔΫͷ֓ཁ ओཁͳΠϯλʔϑΣʔε 02.

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2.1 ϑϨʔϜϫʔΫجຊߏ଄ ग़యɹhttps://medium.com/@imdjay/kotlin-collections-creating-list-set-and-maps-eb3d33500638

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2.1 ϑϨʔϜϫʔΫجຊߏ଄ ग़యɹhttps://medium.com/@imdjay/kotlin-collections-creating-list-set-and-maps-eb3d33500638

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2.1 ϑϨʔϜϫʔΫجຊߏ଄ Iterable Iterableͱ͸ɺίϨΫγϣϯ಺ͷཁૉΛॱ൪ʹऔಘͰ͖ΔΑ͏ʹ͢ΔͨΊͷجຊతͳΠϯ λʔϑΣʔε

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hasNext(): ίϨΫγϣϯ಺ʹ࣍ͷཁૉ͕ଘࡏ͢Δ৔߹͸trueΛฦ͠·͢ɻ next(): ίϨΫγϣϯ಺ͷ࣍ͷཁૉΛฦ͠·͢ɻ Iterator 2.1 ϑϨʔϜϫʔΫجຊߏ଄

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2.1 ϑϨʔϜϫʔΫجຊߏ଄ MutableIterator remove(): ݱࡏͷཁૉΛίϨΫγϣϯ͔Β࡟আ͠·͢

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2.2 ओཁͳΠϯλʔϑΣʔε ग़యɹhttps://medium.com/@imdjay/kotlin-collections-creating-list-set-and-maps-eb3d33500638

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2.2 ओཁͳΠϯλʔϑΣʔε List ॱং෇͚͞ΕͨཁૉͷίϨΫγϣϯͰɺॏෳཁૉΛؚΉ͜ͱ͕Մೳ ΠϯσοΫεΛ࢖༻ͯ͠ΞΫηεͰ͖Δ

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List

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2.2 ओཁͳΠϯλʔϑΣʔε Set ॱং෇͚͞Εͳ͍ཁૉͷίϨΫγϣϯͰɺॏෳཁૉΛؚ·ͳ͍

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2.2 ओཁͳΠϯλʔϑΣʔε Set

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2.2 ओཁͳΠϯλʔϑΣʔε Map ɾΩʔͱ஋ͷϖΞͷίϨΫγϣϯͰɺ֤Ωʔ͸Ұҙ ɾList΍SetͱҧͬͯɺCollectionΠϯλʔϑΣΠεΛ௚઀ʹ͸ܧঝͤͣʹɺಠࣗͰMapΠϯλʔϑΣ ΠεΛ࣋ͭ

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2.2 ओཁͳΠϯλʔϑΣʔε Map

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2.2 ओཁͳΠϯλʔϑΣʔε ग़యɹhttps://medium.com/@imdjay/kotlin-collections-creating-list-set-and-maps-eb3d33500638

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2.2 ओཁͳΠϯλʔϑΣʔε Immutable Mutable ɾKotlinͷίϨΫγϣϯ͸ɺimmutableͱmutableͷόʔδϣϯ͕͋Γ·͢ ɾimmutable͸มߋෆՄɺmutable͸มߋՄೳ ɾmutableʹ͸immutableʹ͸ଘࡏ͠ͳ͍add, removeͱ͍ͬͨมߋͰ͖Δؔ਺͕༻ҙ͞Ε͍ͯ·͢

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ؔ਺ͷ঺հ1 ม׵ɺϑΟϧλϦϯά ཁૉͷ௥Ճɾ࡟আɺάϧʔϓԽ 03.

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Collectionͷجຊૢ࡞Λߦ͏ϝϯόʔؔ਺Λఏڙ͠·͢ɻྫ͑͹ɺCollectionͷ isEmpty()΍Listͷget()͕͋Γ·͢ɻಠࣗͷίϨΫγϣϯΛ࣮૷͢Δࡍʹ͸ɺ͜Ε Βͷϝϯόʔؔ਺΋࣮૷͕ඞཁͰ͢ɻඪ४ϥΠϒϥϦʹ͸ɺ৽͍͠ίϨΫγϣϯ Λ؆୯ʹ࡞੒͢ΔͨΊͷࠎ࣮֨૷΋༻ҙ͞Ε͍ͯ·͢ɻ CollectionͷϑΟϧλϦϯάɺม׵ɺฒ΂ସ͑ͳͲΛߦ͏֦ுؔ਺΋ؚ·Ε͍ͯ· ͢ɻ֦ுؔ਺Λ࢖͏͜ͱͰɺطଘͷίϨΫγϣϯʹ৽͍͠ػೳΛॊೈʹ௥ՃͰ͖ ·͢ɻ ϝϯόʔؔ਺ ֦ுؔ਺

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3.1 ม׵ طଘͷCollection͔Β৽͍͠CollectionΛߏங͠·͢ طଘͷίϨΫγϣϯ͔Β৽͍͠ίϨΫγϣϯΛߏங͠·͢ Map ผͷCollectionͷཁૉʹର͢Δؔ਺ͷ݁Ռ͔ΒCollectionΛ࡞੒ ͠·͢ Zip ྆ํͷCollection಺ͷಉ͡Ґஔʹ͋Δཁૉ͔ΒϖΞΛߏங͠· ͢ Associate CollectionཁૉͱͦΕΒʹؔ࿈෇͚ΒΕͨಛఆͷ஋͔ΒϚοϓ ΛߏஙͰ͖·͢ Flatten ωετ͞ΕͨCollectionΛҰͭͷCollectionʹ͠·͢

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3.1 ม׵ Map ɾCollectionͷ֤ཁૉʹࢦఆͨ͠ม׵ؔ਺Λద༻͠ɺͦͷ݁Ռ͔Β৽͍͠CollectionΛ࡞੒͠·͢ɻ ɾجຊతͳϚοϐϯάؔ਺͸map()Ͱ͢ɻ ɾࢦఆ͞ΕͨϥϜμؔ਺Λ֤ཁૉʹద༻͠ɺϥϜμ݁ՌͷϦετΛฦ͠·͢ɻ ɾ݁Ռͷॱং͸ݩͷཁૉͷॱংͱಉ͡Ͱ͢ɻ map() Signature Ex.

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3.1 ม׵ Map ɾཁૉΠϯσοΫεΛҾ਺ͱͯ͠࢖༻͢Δม׵ʹ͸mapIndexed()Λ࢖༻͠·͢ɻ mapIndexed() Signature Ex.

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3.1 ม׵ ɾม׵ʹΑΓಛఆͷཁૉͰnull͕ੜ੒͞ΕΔ৔߹ ɾmapNotNull()Λ࢖༻͢Δ͜ͱͰɺ݁ՌͷCollection͔ΒnullΛআ֎Ͱ͖·͢ɻ Map mapNotNull() Signature Ex.

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3.1 ม׵ ɾཁૉΠϯσοΫεΛҾ਺ͱͯ͠࢖༻͢Δࡍɺม׵ʹΑΓಛఆͷཁૉͰnull͕ੜ੒͞ΕΔ৔߹ ɾmapIndexedNotNull()Λ࢖༻͢Δ͜ͱͰɺ݁ՌͷCollection͔ΒnullΛআ֎Ͱ͖·͢ɻ Map mapIndexedNotNull() Signature Ex.

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3.1 ม׵ ɾCollectionͷ֤ཁૉʹରͯ͠ࢦఆ͞Εͨม׵ؔ਺Λద༻͠ɺ݁ՌΛࢦఆ͞ΕͨѼઌCollectionʹ௥ Ճ͢Δ ɾ৽͍͠CollectionΛੜ੒͢ΔͷͰ͸ͳ͘ɺطଘͷCollectionʹม׵݁ՌΛ௥Ճ͠·͢ɻ ɾmapIndexedTo(), mapNotNullTo()ͳͲɺଞͷmapܥؔ਺શͯʹto͕͍͍ͭͯ·͢ɻ Map mapTo() Signature Ex.

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3.1 ม׵ Zip ɾZipม׵͸ɺೋͭͷCollection಺ͷಉ͡Ґஔʹ͋Δཁૉ͔ΒϖΞΛߏங͠·͢ɻ ɾ݁ՌͷϖΞͷ࠷ॳͷཁૉ͸ɺReceiver CollectionͷཁૉͰ͢ɻ ɾCollectionͷαΠζ͕ҟͳΔ৔߹ɺ݁Ռ͸খ͍͞ํͷαΠζʹͳΓ·͢ɻ ɾzip()͸ɺa zip bܗࣜͷதஔͰ΋ݺͼग़ͤ·͢ɻ ɾܭࢉྔ͸O(min(n, m)) Signature zip() Ex.

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3.1 ม׵ ɾzip()͸2ͭͷύϥϝʔλʢड৴ଆཁૉͱҾ਺ཁૉʣΛऔΔม׵ؔ਺Λ࢖༻ͯ͠ݺͼग़͢͜ͱ΋Ͱ͖·͢ɻ ɾ͜ͷ৔߹ɺ݁ՌϦετʹ͸ɺड৴ଆཁૉͱҾ਺ཁૉͷϖΞʹରͯ͠ม׵ؔ਺Λద༻ͨ͠໭Γ஋ؚ͕·Ε·͢ɻ Zip zip() Ex. Signature

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3.1 ม׵ ɾϖΞͷϦετ͕͋Δ৔߹͸ɺ͜ΕΒͷϖΞ͔Β 2 ͭͷϦετΛߏங͢Δٯม׵ (ղౚ) Λ࣮ߦͰ͖·͢ɻ Zip unzip() Signature Ex.

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3.1 ม׵ Associate ɾCollectionΛMapʹม׵͢ΔͨΊͷศརͳؔ਺Ͱ͢ associateWith() Signature Ex.

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3.1 ม׵ Associate ɾassociateByؔ਺Ͱ͸ɺCollectionͷ֤ཁૉ͕݁ՌͷϚοϓ಺ͰͲͷΑ͏ʹΩʔͱ஋ͷϖΞʹม׵͞ΕΔ΂͖ ͔Λࢦఆ͢Δ͜ͱ͕Ͱ͖·͢ associateBy() Signature Ex.

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3.1 ม׵ Associate ɾ৽͍͠CollectionΛੜ੒͢ΔͷͰ͸ͳ͘ɺطଘͷMapʹཁૉΛ௥Ճ͠·͢ɻ ɾassociateByTo(), associateWithTo()ͳͲɺଞͷassociateܥؔ਺શͯʹto͕͍͍ͭͯ·͢ɻ associateTo() Signature Ex.

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3.1 ม׵ Associateɹ ஫ҙ఺ ɾPair ObjectΛଟ਺ੜ੒ͯ͠͠·͏͜ͱͷݒ೦ ɹɾ֤Collectionཁૉʹରͯ͠୹໋ͷPair ObjectΛੜ੒͠·͢ɻ͜ΕʹΑΓɺҰ࣌తͳϝϞϦ࢖༻ྔ͕૿Ճ͠·͢ɻ ɹɾେن໛ͳCollectionʹରͯ͠associate()Λ࢖༻͢Δͱɺଟ਺ͷPair Object͕࡞੒͞ΕɺΨϕʔδίϨΫγϣϯͷ ෛ୲͕૿Ճ͢ΔՄೳੑ͕͋Γ·͢ɻ ɹɾPair ObjectΛੜ੒͢Δίετ͕͔͔Γ·͢ɻ֤ཁૉʹରͯ͠ϖΞΛ࡞੒͢ΔͨΊɺଟ਺ͷObjectੜ੒͕ൃੜ͠ ·͢ɻ ɹɾObjectੜ੒ͷΦʔόʔϔου͕ྦྷੵ͢ΔͱɺύϑΥʔϚϯεʹӨڹΛ༩͑Δ͜ͱ͕͋Γ·͢ɻ ɾύϑΥʔϚϯε͕ॏཁͰͳ͍৔߹΍ɺΩʔͱ஋ΛҰॹʹੜ੒͢Δඞཁ͕͋Δ৔߹ʹద͍ͯ͠·͢ɻ

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3.1 ม׵ Flatten ɾωετ͞ΕͨCollectionͷ͢΂ͯͷཁૉͷ୯ҰͷϦετΛฦ͠·͢ɻ Signature Ex. flatten()

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Flatten 3.1 ม׵ Signature Ex. flatMap() ɾCollectionͷ֤ཁૉʹରͯ͠ࢦఆ͞Εͨม׵ؔ਺Λద༻͠ɺͦͷ݁Ռͱͯ͠ಘΒΕͨCollectionΛ Ұͭʹ·ͱΊͯฏୱԽ͠·͢ɻ ɾܭࢉྔ͸O(n + m) ɹɾn͸ݩͷίϨΫγϣϯͷཁૉ਺ɻ ɹɾm͸ม׵͞ΕͨίϨΫγϣϯͷશཁૉ਺ͷ߹ܭɻ ɾΦʔόʔϔου ɹɾ֤ཁૉʹରͯ͠ϦετΛੜ੒͢ΔͨΊɺෆཁͳΦʔόʔϔου͕ൃੜ͢ΔՄೳੑ͕͋Γ·͢ɻ

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3.2 ϑΟϧλϦϯά طଘͷCollectionΛϑΟϧλʔ͠ɺ৽͍͠CollectionΛߏங͠·͢ filter(), filterNot() جຊతͳϑΟϧλϦϯάɻ৚݅ʹ߹க͢Δ͔ɺ͠ͳ͍͔ͰϑΟϧλϦ ϯά͠·͢ɻ filterIndexed() Indexͱ஋ʹج͍ͮͯཁૉΛϑΟϧλϦϯά͠·͢ɻ filterIsInstance(), filterNotNull() ಛఆͷܕͷཁૉ ɺnull஋Λߟྀͯ͠ϑΟϧλϦϯά͠·͢ɻ partition() ৚݅ʹ߹க͢Δཁૉͱ͠ͳ͍ཁૉΛ2ͭͷϦετʹ෼͚·͢ɻ any(), none(), all() Collection಺ͷཁૉ͕৚݅ʹ߹க͢Δ͔Ͳ͏͔ΛνΣοΫ͠·͢ɻ filterTo() طଘͷCollectionʹϑΟϧλϦϯά݁ՌΛ௥Ճ͠·͢ɻ

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3.2 ϑΟϧλϦϯά filter() Signature Ex. ɾ৚݅ʹ߹க͢ΔཁૉΛϦετͰฦ͠·͢ɻ

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3.2 ϑΟϧλϦϯά filterNot() Signature Ex. ɾ৚݅ʹ߹க͠ͳ͍ཁૉΛϦετͰฦ͠·͢ɻ

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3.2 ϑΟϧλϦϯά filterIndexed() Signature Ex. ɾΠϯσοΫεͱ஋ʹج͍ͮͯཁૉΛϑΟϧλϦϯά͠·͢ɻ

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3.2 ϑΟϧλϦϯά filterIsInstance() Signature Ex. ɾಛఆͷܕͷཁૉΛϑΟϧλϦϯά͠·͢ɻ

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3.2 ϑΟϧλϦϯά filterNotNull() Signature Ex. ɾnullҎ֎ͷཁૉΛϑΟϧλϦϯά͠·͢ɻ

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3.2 ϑΟϧλϦϯά filterTo() Signature Ex. ɾطଘͷCollectionʹϑΟϧλϦϯά݁ՌΛ௥Ճ͠·͢ɻ ɾfilterNotTo(), filterNotNullTo(), filterIsInstanceTo(), filterIndexedTo(),΋ଘࡏ͢Δ

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partition() Signature Ex. 3.2 ϑΟϧλϦϯά ɾ৚݅ʹ߹க͢Δཁૉͱ͠ͳ͍ཁૉΛ2ͭͷϦετʹ෼͚·͢ɻ

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3.2 ϑΟϧλϦϯά any() Signature Ex. ɾCollection಺ͷཁૉ͕৚݅ʹ߹க͢Δ΋ͷ͕͋Δ͔ΛνΣοΫ͠·͢ɻ

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3.2 ϑΟϧλϦϯά all() Signature Ex. ɾCollection಺ͷཁૉ͕৚݅ʹશͯ߹க͢Δ͔Ͳ͏͔ΛνΣοΫ͠·͢ɻ

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3.2 ϑΟϧλϦϯά none() Signature Ex. ɾCollection಺ͷཁૉ͕৚݅ʹશͯ߹க͍ͯ͠ͳ͍͔Ͳ͏͔ΛνΣοΫ͠·͢ɻ

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3.3 ཁૉͷ௥Ճɾ࡟আ Collectionʹରͯ͠+ʢplusʣͱ-ʢminusʣԋࢉࢠ͕ఆٛ͞Ε͍ͯ·͢ɻ ͜ΕΒ͸৽͍͠ಡΈऔΓઐ༻ͷCollectionΛฦ͠·͢ɻ Ex. ※ ৽͘͠listΛੜ੒͢Δ෼ɺϝϞϦΛফඅ͠·͢ɻϝϞϦ͕ݫ͍͠৔߹͸ mutableListΛ࢖͏ݕ౼ͳͲ͠·͠ΐ͏ɻ

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3.4 άϧʔϓԽ groupBy() ࢦఆͨ͠Ωʔબ୒ؔ਺ʹΑͬͯཁૉΛάϧʔϓԽ͠ɺϚοϓͱͯ͠ฦ ͠·͢ɻ groupingBy() άϧʔϓԽΛ஗Ԇ࣮ߦ͢ΔGroupingΠϯελϯεΛฦ͠ɺ eachCount()ɺfold()ɺreduce(), aggregate()ͳͲͷૢ࡞Λαϙʔτ͠ ·͢ɻ

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3.4 άϧʔϓԽ Signature Ex. groupBy() ɾطଘͷCollectionΛࢦఆ͞ΕͨΩʔʹج͍ͮͯάϧʔϓԽ͠ɺMapͱͯ͠ฦ͠·͢ɻ

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3.4 άϧʔϓԽ Signature Ex. groupBy() ɾطଘͷCollectionΛࢦఆ͞ΕͨΩʔʹج͍ͮͯάϧʔϓԽ͠ɺvalueTransformͰݩͷཁૉΛมߋ͠Mapͱͯ͠ฦ͠ ·͢ɻ

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3.4 άϧʔϓԽ groupingBy() Signature ɾ஗ԆධՁΛߦ͍ɺதͰGroupingΦϒδΣΫτΛੜ੒͍ͯ͠·͢ɻऴ୺ॲཧͰMapΛฦ͠·͢ɻ

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3.4 άϧʔϓԽ groupingBy() Signature ɾgroupingByΛ࣮ߦ͚ͨͩ͠Ͱ͸άϧʔϓԽ͸ى͜Γ·ͤΜɻeachCount()ɺfold()ɺreduce(), aggregate()ͳͲͷऴ୺ؔ਺Λ࣮ߦͯ͠ॳΊͯgroupingԽ͞Ε·͢ɻ Ex.

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3.4 άϧʔϓԽ groupingBy{}.eachCount() Signature Ex. ɾ֤άϧʔϓͷཁૉ਺ΛΧ΢ϯτ͢ΔϝιουͰ͢ɻ ɾgroupingByͰάϧʔϓԽͨ͠ޙʹeachCountΛݺͼग़͢ͱɺ֤άϧʔϓͷΩʔͱͦͷཁૉ਺ΛϚοϓ ͱͯ͠ฦ͠·͢

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groupingBy{}.reduce() 3.4 άϧʔϓԽ Signature Ex. ɾάϧʔϓ͝ͱͷཁૉΛྦྷੵ͠ɺ୯Ұͷ஋ʹू໿͢ΔͨΊʹ࢖༻͞Ε·͢ɻ ɾ֤άϧʔϓͷ࠷ॳͷཁૉΛॳظ஋ͱ͠ɺࢦఆͨ͠ૢ࡞Λద༻͠·͢ɻ

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groupingBy{}.fold() 3.4 άϧʔϓԽ Signature Ex. ɾ֤άϧʔϓʹରͯ͠ྦྷੵૢ࡞Λߦ͏ͨΊʹ࢖༻͞Ε·͢ɻ ɾॳظ஋ͱྦྷੵؔ਺Λࢦఆͯ͠ɺ֤άϧʔϓͷཁૉΛॱ࣍ॲཧ͠ɺྦྷੵ݁ՌΛੜ੒͠·͢ɻ

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groupingBy{}.aggregate() 3.4 άϧʔϓԽ Signature Ex. ɾάϧʔϓ͝ͱʹΧελϜूܭૢ࡞Λߦ͏ͨΊͷؔ਺Ͱ͢ɻ ɾreduce΍foldͰ࣮ݱ͕೉͍͠৔߹ͷΧελϜૢ࡞ͱͯ͠࢖͑·͢ɻ

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groupingBy{} .aggregate() 3.4 άϧʔϓԽ

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3.4 άϧʔϓԽ groupByTo() ɾطଘͷMapʹάϧʔϓԽ͞ΕͨཁૉΛ௥Ճ͠·͢ɻ ɾgroupingByͷeachCount, fold, reduce, aggregateʹ΋Toϝιου͸ଘࡏ͢Δ Signature Ex.

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4.1 ෦෼औಘ slice() ࢦఆͨ͠ΠϯσοΫεͷϦετΛجʹ৽͍͠ϦετΛ࡞੒͠·͢ɻ take() Ϧετͷઌ಄͔Βࢦఆͨ͠਺ͷཁૉΛऔಘ͠·͢ɻ drop() Ϧετͷઌ಄͔Βࢦఆͨ͠਺ͷཁૉΛআ֎ͨ͠࢒ΓΛऔಘ͠·͢ɻ chunked() ϦετΛࢦఆͨ͠αΠζͷνϟϯΫʢখ͞ͳ෦෼ʣʹ෼ׂ͠·͢ɻ windowed() ࢦఆͨ͠αΠζͷ΢Οϯυ΢ʢεϥΠσΟϯά෦෼ʣΛϦετ͔Β ੜ੒͠·͢ɻ طଘͷCollection͔ΒҰ෦ΛऔΓग़͠ɺsublistΛੜ੒͠·͢ɻ

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4.1 ෦෼औಘ slice() Signature Ex. ɾCollection಺ͷཁૉ͕৚݅ʹશͯ߹க͢Δ͔Ͳ͏͔ΛνΣοΫ͠·͢ɻ ɾܭࢉྔ͸O(n) ɾࢦఆͨ͠ΠϯσοΫεͷϦετΛجʹ৽͍͠ϦετΛ࡞੒͠·͢ɻ ɾҾ਺͸IntRangeͱIterableͷ̎ύλʔϯ͋Γ·͢ɻ

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4.1 ෦෼औಘ take() takeLast() Signature Ex. ɾϦετͷઌ಄͔Βࢦఆͨ͠਺ͷཁૉΛऔಘ͠·͢ɻ ɾtakeLast͸Ϧετͷ຤ඌ͔Βࢦఆͨ͠਺ͷཁૉΛऔಘ͠·͢ɻ

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4.1 ෦෼औಘ takeWhile() takeLastWhile() Signature Ex. ɾࢦఆ͞Εͨ৚͕݅ਅͰ͋ΔݶΓɺCollectionͷཁૉΛઌ಄͔Βॱʹऔಘ͠·͢ɻ ɾtakeLast͸ࢦఆ͞Εͨ৚͕݅ਅͰ͋ΔݶΓɺCollectionͷཁૉΛ຤ඌ͔Βॱʹऔಘ͠·͢ɻ

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4.1 ෦෼औಘ Signature Ex. drop() dropLast() ɾϦετͷઌ಄͔Βࢦఆͨ͠਺ͷཁૉΛআ֎ͨ͠࢒ΓΛऔಘ͠·͢ɻ ɾdropLast͸Ϧετͷ຤ඌ͔Βࢦఆͨ͠਺ͷཁૉΛআ֎ͨ͠࢒ΓΛऔಘ͠·͢ɻ

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4.1 ෦෼औಘ dropWhile() dropLastWhile() Signature Ex. ɾࢦఆ͞Εͨ৚͕݅ਅͰ͋ΔݶΓɺCollectionͷཁૉΛઌ಄͔Βॱʹআ֎͠·͢ɻ ɾdropLast͸ࢦఆ͞Εͨ৚͕݅ਅͰ͋ΔݶΓɺCollectionͷ຤ඌ͔ΒॱʹཁૉΛআ֎͠·͢ɻ

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chunked() 4.1 ෦෼औಘ Signature Ex. ɾCollectionΛࢦఆͨ͠αΠζͷνϟϯΫʢখ͞ͳ෦෼ʣʹ෼ׂ͠·͢ɻ ɾνϟϯΫͨ͠ޙʹɺtransform͢Δࣄ΋ՄೳͰ͢ ɾେྔͷσʔλΛҰ౓ʹॲཧ͢ΔͷͰ͸ͳ͘ɺগͣͭ͠ޮ཰తʹॲཧ͍ͨ࣌͠ʹ˕

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4.1 ෦෼औಘ windowed() Signature Ex. ɾࢦఆͨ͠αΠζͷ΢Οϯυ΢ʢεϥΠσΟϯά෦෼ʣΛϦετ͔Βੜ੒͠·͢ ɾ෼ׂͨ͠ޙʹɺtransform͢Δࣄ΋ՄೳͰ͢ ɾܭࢉྔ: O(n * k) ʢn͸ݩͷϦετͷαΠζɺk͸΢Οϯυ΢ͷαΠζʣ

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4.1 ෦෼औಘ windowed() ɾؔ਺ͷ໊લɺwindowedͷ֓೦͸ɺ࿈ଓత·ͨ͸௕͍σʔλγʔέϯεΛখ͞ͳʮ΢Οϯυ΢ʯʹ෼ׂɻ ɾͦΕͧΕͷ΢Οϯυ΢ʢࠓ૭͔Βݟ͍͑ͯΔ෦෼ʣʹରͯ͠ݸผʹॲཧΛߦ͏ͱ͍͏ํ๏࿦ʹج͍͍ͮͯ·͢ɻ ग़యɹhttps://www.baeldung.com/kotlin/collections-api

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4.2 ୯Ұཁૉऔಘ first() Collectionͷ࠷ॳͷཁૉΛऔಘ last() Collectionͷ࠷ޙͷཁૉΛऔಘ elementAt() ࢦఆ͞ΕͨindexͷཁૉΛऔಘ

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4.1 ෦෼औಘ Signature Ex. first() ɾCollectionͷ࠷ॳͷཁૉΛऔಘ͠·͢ɻ৚݅Λࢦఆ͢Δ͜ͱ΋ՄೳͰ͢ɻ ɾແ͚Ε͹NoSuchElementException͕throw͞ΕΔͷͰ஫ҙ

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4.1 ෦෼औಘ Signature Ex. last() ɾCollectionͷ࠷ޙͷཁૉΛऔಘ͠·͢ɻ৚݅Λࢦఆ͢Δ͜ͱ΋ՄೳͰ͢ɻ ɾແ͚Ε͹NoSuchElementException͕throw͞ΕΔͷͰ஫ҙ

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4.1 ෦෼औಘ Signature Ex. firstOrNull() ɾCollectionͷ࠷ॳͷཁૉΛऔಘ͠·͢ɻ৚݅Λࢦఆ͢Δ͜ͱ΋ՄೳͰ͢ɻ ɾແ͚Ε͹null͕ฦ͖ͬͯ·͢ɻ

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å 4.1 ෦෼औಘ Signature Ex. lastOrNull() ɾCollectionͷ࠷ޙͷཁૉΛऔಘ͠·͢ɻ৚݅Λࢦఆ͢Δ͜ͱ΋ՄೳͰ͢ɻ ɾແ͚Ε͹null͕ฦ͖ͬͯ·͢ɻ

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4.1 ෦෼औಘ Signature Ex. firstNotNullOf() ɾCollection಺ͷཁૉΛࢦఆ͞Εͨม׵ؔ਺Λద༻͠ɺ࠷ॳͷඇnullͷ݁ՌΛฦ͠·͢ɻ ɾແ͚Ε͹NoSuchElementException͕throw͞ΕΔͷͰ஫ҙ

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4.1 ෦෼औಘ Signature Ex. firstNotNullOfNull() ɾCollection಺ͷཁૉΛࢦఆ͞Εͨม׵ؔ਺Λద༻͠ɺ࠷ॳͷඇnullͷ݁ՌΛฦ͠·͢ɻ ɾແ͚Ε͹null͕ฦ͖ͬͯ·͢

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4.1 ෦෼औಘ elementAt() elementAtOrNull() elementAtOrElse() ɾࢦఆ͞ΕͨindexͷཁૉΛऔಘ͠·͢ɻ ɾelementAt()͸ࢦఆ͞Εͨindex͕listͷൣғ֎ͩͬͨ৔߹IndexOutOfBoundsException͕throw ɾelementAtOrNull()͸ࢦఆ͞Εͨindex͕listͷൣғ֎ͩͬͨ৔߹null ɾelementAtOrElse()͸ࢦఆ͞Εͨindex͕listͷൣғ֎ͩͬͨ৔߹ࢦఆͨ͠default஋

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4.3 ฒͼସ͑ sorted() ࣗવॱংʹج͍ͮͯཁૉΛιʔτ͠·͢ sortedDescending() ࣗવॱংʹج͍ͮͯཁૉΛ߱ॱʹιʔτ͠·͢ sortedBy() ࢦఆͨ͠ηϨΫλʔؔ਺ʹج͍ͮͯཁૉΛιʔτ͠·͢ sortedByDescending() ࢦఆͨ͠ηϨΫλʔؔ਺ʹج͍ͮͯཁૉΛ߱ॱʹιʔτ͠ ·͢ sortedWith() ࢦఆͨ͠ίϯύϨʔλʹج͍ͮͯཁૉΛιʔτ͠·͢ reversed() ཁૉͷॱংΛ൓సͤ͞·͢ shuffled() ཁૉΛϥϯμϜʹฒ΂ସ͑·͢

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sorted() sortedDescending() ɾsorted()͸ঢॱʹsort͠·͢ ɾsortedDescending()͸߱ॱʹsort͠·͢ 4.3 ฒͼସ͑

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sortedBy() sortedByDescending() ɾsortedByؔ਺͸ɺࢦఆͨ͠ϓϩύςΟΛج४ʹCollectionͷཁૉΛঢॱʹsort͠·͢ɻ ɾsortedByDescendingؔ਺͸ɺࢦఆͨ͠ϓϩύςΟΛج४ʹίϨΫγϣϯͷཁૉΛ߱ॱʹsort͠·͢ɻ 4.3 ฒͼସ͑

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sortedWith() ɾsortedWithؔ਺͸ɺࢦఆͨ͠ComparableΛ࢖ͬͯίϨΫγϣϯͷཁૉΛsort͠·͢ɻ ɾ͜ͷαϯϓϧͰ͸ɺcompareByͱthenByΛ࢖ͬͯComparableΛ࡞੒͠ɺsortedWithؔ਺ ʹ౉͍ͯ͠·͢ɻ·ͣɺ໊લΛج४ʹsort͠ɺ࣍ʹ೥ྸΛج४ʹsort͍ͯ͠·͢ɻ 4.3 ฒͼସ͑

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reserved()  asReserved() ɾreserved()΋asReserved()΋originalͷCollectionΛมߋͤͣʹٯॱʹฒ΂ସ͑ͨ஋Λฦ͠·͢ɻ ɾreserved()͸৽͍͠ϦετΛฦ͠ɺasReserved()͸ݩͷϦετΛࢀরͯ͠࡞੒͢ΔͨΊɺ৽͍͠Ϧετ ͸࡞੒͠ͳ͍ ɹɾCollectionͷن໛͕େ͖͍ͱasReserved()ͷํ͕ϝϞϦޮ཰ɺ࣮ߦ଎౓͕ૣ͍৔߹͕͋Γ·͢ɻ 4.3 ฒͼସ͑

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asReserved() ɾasReserved͸ࢀরͷindexΛٯॱʹ͍ͯ͠Δ͚ͩͰ࣮ݱ͍ͯ͠·͢ɻ৽͍͠list͸࡞੒͠ͳ͍ɻ 4.3 ฒͼସ͑

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shuffled() 4.3 ฒͼସ͑ ɾϦετͷཁૉΛϥϯμϜʹγϟοϑϧͯ͠৽͍͠ϦετΛ࡞੒͠·͢ɻݩͷϦετ͸มߋ͞Ε·ͤΜɻ ɾϥϯμϜγʔυΛࢦఆͯ͠γϟοϑϧΛߦ͏͜ͱͰɺ࠶ݱՄೳͳγϟοϑϧ݁ՌΛಘΔ͜ͱ΋Ͱ͖·͢ɻ

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4.4 ू໿ؔ਺ maxOrNull() CollectionͷཁૉͷதͰ࠷େͷ΋ͷΛฦ͠·͢ minOrNull() CollectionͷཁૉͷதͰ࠷খͷ΋ͷΛฦ͠·͢ sum() CollectionͷཁૉΛ߹ܭ͢ΔͨΊʹ࢖༻͞Ε·͢ average() Collectionͷ਺஋ཁૉͷฏۉΛܭࢉ͢ΔͨΊʹ࢖༻͞Ε·͢ count() Collectionͷཁૉͷ਺Λ਺͑ΔͨΊʹ࢖༻͞Ε·͢ fold() ॳظ஋ͱྦྷੵૢ࡞Λࢦఆͯ͠ࠨ͔ΒӈʹίϨΫγϣϯΛંΓͨͨΉɻ reduce() ॳظ஋ͳ͠Ͱ࠷ॳͷཁૉΛॳظ஋ͱͯ͠ࠨ͔ΒӈʹίϨΫγϣϯΛॖখ͢ Δɻ

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maxOrNull() ɾCollectionͷཁૉͷதͰ࠷େͷཁૉΛฦ͠·͢ɻ ɾCollectionͷཁૉ͕ແ͚Ε͹nullΛฦ͠·͢ɻ ɾmax()ؔ਺͸ඇਪ঑ͱͳͬͯ·͢ɻ 4.4 ू໿ؔ਺

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maxByOrNull() ɾΧελϜΦϒδΣΫτͷϓϩύςΟΛج४ʹͯ͠࠷େ஋Λ؆୯ʹऔಘͰ͖·͢ɻ 4.4 ू໿ؔ਺

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4.4 ू໿ؔ਺ minOrNull() ɾCollectionͷཁૉͷதͰ࠷খͷཁૉΛฦ͠·͢ɻ ɾCollection͕ແ͚Ε͹nullΛฦ͠·͢ɻ ɾmin()ؔ਺͸ඇਪ঑ͱͳͬͯ·͢ɻ

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4.4 ू໿ؔ਺ minByOrNull() ɾΧελϜΦϒδΣΫτͷϓϩύςΟΛج४ʹͯ͠࠷খ஋Λ؆୯ʹऔಘͰ͖·͢ɻ

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4.4 ू໿ؔ਺ sum() ɾCollectionͷཁૉͷ߹ܭΛฦ͠·͢ɻ

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4.4 ू໿ؔ਺ sumOf() ɾΧελϜΦϒδΣΫτͷϓϩύςΟΛج४ʹͨ͠߹ܭ஋ͷऔಘ͕Ͱ͖·͢ɻ

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4.4 ू໿ؔ਺ average() ɾCollection಺ͷ਺஋ͷฏۉ஋Λܭࢉ͢ΔͨΊʹ࢖༻͞Ε·͢ɻ ɾۭͷCollectionͷ৔߹ɺaverage()ؔ਺͸NaNʢNot a NumberʣΛฦ͠·͢ɻ

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4.4 ू໿ؔ਺ count() ɾCollectionͷཁૉͷ਺Λऔಘ ɾಛఆͷ৚݅Λຬͨ͢ཁૉͷ਺ΛΧ΢ϯτ͢Δ৔߹͸ɺϥϜμࣜΛcount()ؔ਺ʹ౉͠·͢ɻ

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4.4 ू໿ؔ਺ fold() ɾCollectionͷཁૉΛࠨ͔Βӈ΁ॱʹ৞ΈࠐΈʢྦྷੵ͠ʣͳ͕Βૢ࡞Λߦ͏ͨΊʹ࢖༻͞Ε·͢ɻ ɾॳظ஋ͱྦྷੵ݁ՌΛอ࣋͢ΔͨΊͷؔ਺Λड͚औΓ·͢ɻ ɾfoldRight()͸foldͱ͸ٯॱʹཁૉΛ߹ܭ͍͖ͯ͠·͢ɻ

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4.4 ू໿ؔ਺ reduce() ɾCollectionͷཁૉΛࠨ͔Βӈ΁ॱʹ৞ΈࠐΈʢྦྷੵ͠ʣͳ͕Βૢ࡞Λߦ͏ͨΊʹ࢖༻͞Ε·͢ɻ ɾfold()ͱͷҧ͍͸ॳظ஋͕ͳ͍͜ͱ

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ߴ౓ͳؔ਺ͷ࢖༻ྫ chunked windowed 05.

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5.1 chunked Signature Ex. ɾCollectionΛࢦఆͨ͠αΠζͷνϟϯΫʢখ͞ͳ෦෼ʣʹ෼ׂ͠·͢ɻ

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5.1 chunked σʔλϕʔε΁ͷ όονૠೖ ɾେྔʹҰ౓ʹૠೖ͢ΔͱύϑΥʔϚϯε͕མͪͯ͠·͏৔߹ʹখ෼͚ʹ͢Δ

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5.1 chunked େྔͷը૾ μ΢ϯϩʔυ ɾອըͷμ΢ϯϩʔυͳͲɺେྔͷը૾μ΢ϯϩʔυΛ͢Δࡍɺখ෼͚ʹ࣮ͯ͠ߦ͕؆୯ʹͰ͖Δ

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5.2 windowed Signature Ex. ɾࢦఆͨ͠αΠζͷ΢Οϯυ΢ʢεϥΠσΟϯά෦෼ʣΛϦετ͔Βੜ੒͠·͢

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5.2 windowed Ҡಈฏۉઢ ɾ࣌ܥྻσʔλʹରͯ͠ҠಈฏۉΛܭࢉ͢Δ৔߹ɺwindowedؔ਺͸ඇৗʹศརͰ͢ɻ

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5.2 windowed ύλʔϯݕग़ ɾςΩετ΍਺ྻͷதͰಛఆͷύλʔϯΛݕग़͢ΔࡍʹɺwindowedΛ࢖ͬͯ࿈ ଓ͢Δ෦෼ΛνΣοΫͰ͖·͢ɻ

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ࠩ෼ͷܭࢉ 5.2 windowed ɾ਺ྻͷྡ઀͢Δཁૉؒͷࠩ෼Λܭࢉ͢Δ৔߹ʹ΋windowed͕໾ཱͪ·͢ɻ

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Ի੠ͷղੳ 5.2 windowed

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ύϑΥʔϚϯεͷ࠷దԽ sequence forจ 06.

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6.1 Sequenceͱforจ ɾSequence͸஗ԆධՁΛߦ͏Collection typeͰେྔͷσʔλॲཧʹ͓͍ͯޮ཰తͰ͢ ɾSequence͸ཁૉΛҰͭͣͭॲཧ͠ɺதؒૢ࡞͸஗Ԇ͞Εɺ࠷ऴૢ࡞͕ݺ͹ΕΔ·Ͱ࣮ߦ ͞Ε·ͤΜɻ͜ΕʹΑΓɺதؒૢ࡞ͷແବͳܭࢉΛආ͚Δ͜ͱ͕Ͱ͖·͢ɻ Sequence

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ύϑΥʔϚϯεൺֱɹCollection, Sequence, for IntegerͷϦετʹରͯ͠Լهͷ࣮ߦΛߦ͍·͢ɻ IntegerͷϦετͷαΠζ͸ෳ਺࣮ࢪɻ ɾۮ਺ͷΈΛநग़ɻ ɾ͞Βʹɺͦͷத͔Β3ͰׂΓ੾ΕΔ਺Λநग़ʢ6ͷഒ਺ʣɻ ɾͦΕΒͷ਺Λೋ৐ɻ ɾ࠷ॳͷ5ݸͷཁૉΛऔΓग़͢ɻ 6.1 Sequenceͱforจ

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Collection 6.1 Sequenceͱforจ

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Sequence 6.1 Sequenceͱforจ

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for 6.1 Sequenceͱforจ

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ɾSequence͸ϦετͷαΠζ͕૿͑ͯ΋࣮ߦ଎౓͸΄΅มΘΒͳ͍͕ɺϦετ͕খͯ͘͞΋overhead͕ଘࡏͯ͠͠·͏ ɾCollection͸ϦετͷαΠζ͕૿͑Δͱൺྫͯ͠૿͑ΔɻϦετ͕େ͖͘ͳ͍࣌͸SequenceΑΓ΋ૣ͍ ɾforจ͸࠷଎ 6.1 Sequenceͱforจ Kotlin PlaygroundͰͷ10ճฏۉ

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SequenceͱCollectionͷҧ͍ ɾCollection: ଈ࣌ධՁΛߦ͍ɺશͯͷཁૉΛϝϞϦʹอ࣋͠ɺॲཧ͠·͢ɻ ɾSequence: ஗ԆධՁΛߦ͍ɺඞཁͳཁૉͷΈΛॲཧ͠·͢ɻ 6.1 Sequenceͱforจ

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Sequenceͷૢ࡞ தؒૢ࡞: ऴ୺ૢ࡞: தؒૢ࡞͸஗ԆධՁ͞ΕΔૢ࡞Ͱ͢ɻྫ͑͹ɺmapɺfilterɺͳ Ͳؚ͕·Ε·͢ɻ͜ΕΒͷૢ࡞͸৽͍͠γʔέϯεΛฦ͠ɺ࣮ࡍ ͷॲཧ͸ऴ୺ૢ࡞͕ݺͼग़͞ΕΔ·ͰߦΘΕ·ͤΜɻ ऴ୺ૢ࡞͸SequenceΛফඅͯ݁͠ՌΛੜ੒͢Δૢ࡞Ͱ͢ɻྫ͑ ͹ɺtoListɺsumɺcountɺfirstͳͲ͕͋Γ·͢ɻऴ୺ૢ࡞͕ݺ͹ ΕΔͱɺશͯͷதؒૢ࡞͕࣮ߦ͞Ε·͢ɻ 6.1 Sequenceͱforจ

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Collection 6.1 Sequenceͱforจ

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Collection 6.1 Sequenceͱforจ

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Sequence 6.1 Sequenceͱforจ

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Sequence 6.1 Sequenceͱforจ

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Sequence 6.1 Sequenceͱforจ ऴ୺ͷiterateͰCollectionͷཁૉ͝ͱʹॲཧΛ͍ͯ͠·͢ɻ

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Sequenceͷ࢖͍ॴ 1. ͔ͳΓେن໛ͳίϨΫγϣϯʹରͯ͠ෳ਺ͷॲཧΛߦ͏৔߹ 2. ଟஈνΣʔϯΛల։͠ɺதؒϦετͷੜ੒Λආ͚͍ͨ৔߹ 3. ύϑΥʔϚϯεͱϝϞϦ࢖༻ྔΛ࠷దԽ͍͕ͨ͠ɺforจΛ࢖͍ͨ͘ͳ͍৔߹ 6.1 Sequenceͱforจ

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6.2 ·ͱΊ ɾCollectionؔ਺͸༏लͳͷͰɺجຊతʹCollectionؔ਺Λ࢖͍·͠ΐ͏ɻ ɾϦετͷαΠζ͕େ͖͘ύϑΥʔϚϯεͷϘτϧωοΫ͕͋ΓɺՄಡੑΛ ҡ͍࣋ͨ͠৔߹ʹSequenceΛ࢖༻ ɾ࠷଎ΛٻΊΔͳΒforจ

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Special Thanks KotlinެࣜϦϑΝϨϯε https://kotlinlang.org/docs/collections-overview.html Effective Kotlin: Prefer Sequence for big collections with more than one processing step https://blog.kotlin-academy.com/effective-kotlin-use-sequence-for-bigger-collections-with-more-than-one- processing-step-649a15bb4bf

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