いつか役にたつかもしれないコレクション周りの5つのこと

Transcript

1. 1.

   ผʹܶతʹ͸มΘΒͳ͍͚ΕͲ ͍͔ͭ໾ʹ͔ͨͭ΋͠Εͳ͍ ίϨΫγϣϯपΓͷ5ͭͷ͜ͱ @RyotaMurohoshi 2016/07/05(Ր)*͸͡ΊͯͷKotlin

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   ͦͷ1 ঢ়گʹԠͯ͡SequenceΛ࢖͏΂͖ͳ݅

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   100000ߦͷJSON'LinesϑΝΠϧ ͜ΕΛ1ߦͣͭdataΫϥεͷΦϒδΣΫτʹม׵͠ ͋Δ৚݅Λຬͨ͢ΦϒδΣΫτΛ ࠷ॳ͔Β10͚݅ͩ֬ೝද͍ࣔͨ͠

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   List<T>ͷ৔߹

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   val lineList: List<String> = File("data.jsonlines").readLines() val result = lineList .map

   { convertToData(it) } .filter { filterData(it) } .take(10) for (it in result) { println(it) }
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   ࠷ޙ·ͰϑΝΠϧΛಡΜͰ͠·͏

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   Sequence<T>ͷ৔߹

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   val result: List<PersonData> = File("data.jsonlines") .useLines { lineSequences: Sequence<String> ->

   lineSequences .map { convertToData(it) } .filter { filterData(it) } .take(10) .toList() } for (it in result) { println(it) }
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   ϑΝΠϧΛ࠷ޙ·Ͱಡ·ͳ͍

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    ৄ͘͠͸͜ͷࢿྉͰʂ h"ps:/ /speakerdeck.com/ryotamurohoshi/sequencefalsehua8kotlin8dot8sequences8dot8sequence

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    ͦͷ2 ཁૉ͕ۭͷ࣌ͷaverageϝιου͕ 0.0Λฦͯ͠͠·͏݅

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    averageϝιουͱ͸ʁ List<Int>ͱ͔ͷฏۉܭࢉϝιου

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    ͡Ό͋ɺཁૉ͕ۭͷ࣌͸ʁ

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    ·͔͞ͷ0.0!

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    ͳͥͩʂʁ

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    ͜Ε͡Όܭࢉ݁Ռ͕0.0ͩͬͨͷ͔ɺ ཁૉ͕ۭ͔ͩΒ0.0ͬͨͷ͔ ۠ผԽ͔ͭͳ͍ʂʂʂ

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    ͦ΋ͦ΋ͳͥDouble?ܕʹ͠ͳ͔ͬͨͷ͔ʁ max΍min͸Int?Λฦ͢ͷʹʂ ΋͘͠͸ྫ֎Λ౤͛ͯཉ͍͠

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    ͦͷ3 Ωʔ͕ॏෳͨ͠ࡍͷassociateܥϝιου͕ɺ ྫ֎Λ౤͛ͳ͍݅

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    associateܥͷϝιουͱ͸ʁ Listͱ͔͔ΒMapΛͭ͘Δϝιου

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    data class Person( val id: Long,ɹval name: String, val teamId:

    Long) // ॏෳidͷPerson͸ଘࡏ͠ͳ͍ // ಉ͡teamIdΛ࣋ͭPerson͸ଘࡏ͠͏Δ val personList : List<Person>ɹ= loadPersonList() // id͕ॏෳ͸͠ͳ͍ͷͰ໰୊ແ͠ val personMap : Map<Long, Person> = personList.associateBy { it.id } // ʲ஫໨ʂʂʂʳಉ͡teamIdΛ΋ͭཁૉ͕personList಺ʹଘࡏ͠͏Δʂʂʂʂʂ val teamMap : Map<Long, Person> = personList.associateBy { it.teamId }
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    ΋͠Key͕ॏෳͨ͠Βʁ

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    ޙউʂ ͋ͱ͕ͪ:ޙΖͷཁૉͰ্ॻ͖

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    ݸਓతʹ͸ྫ֎Λ౤͛ͯཉ͍͠

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    ͦ΋ͦ΋MapΛͭ͘ͷͰ͋Ε͹ɺKey͸Ұҙͳ΋ͷͳ͸ͣ Key͕ॏෳ͢Δ΋ͷΛ૝ఆ͢ΔͳΒ͹ɺgroupByΛ࢖͏΂͖

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    ಥવͷએ఻

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    C#ͷLINQޓ׵ͷϥΠϒϥϦ KotLinq࡞͍ͬͯ·͢ʂʂʂ h"ps:/ /github.com/RyotaMurohoshi/KotLinq

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    ࠓճͷTips͸ KotLinqΛ࡞͍ͬͯΔࡍͷ஌ݟͰ͢

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    ͦͷ4 σϑΥϧτΠϯϙʔτ֦ுؔ਺Λ ্ॻ͖Ͱ͖Δ݅

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    ࣗ࡞ϥΠϒϥϦKotLinqͷ಺ʹ͸ takeͬͯϝιου͕͋Γ·͢ʂ

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    KotLinq಺ͷtakeϝιου fun <TSource> Iterable<TSource>.take(count: Int): Sequence<TSource> = asSequence().take(count)

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    Μʁ

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    ඪ४ؔ਺ʹ΋takeͬͯ͋ͬͨΑ͏ͳ? fun <T> Iterable<T>.take(n: Int): List<T>

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    ඪ४ͰΠϯϙʔτͰ͖Δ֦ுؔ਺ Λ্ॻ͖Ͱ͖Δ݅ʂ

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    ͦͷ5 ϝιουͷΦʔόʔϩʔυͱit͕ ૬ੑѱ͍݅ (͜Ε͋Μ·ΓίϨΫγϣϯؔ܎ͳ͍)

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    ࣹӨϝιου!ͱ!ΠϯσοΫε෇͖ࣹӨϝιουೋͭ࡞Γ͍ͨ // ࣹӨϝιου fun <TSource, TResult> Sequence<TSource> .select(selector: (TSource) ->

    TResult): Sequence<TResult> // ΠϯσοΫε෇͖ࣹӨϝιου fun <TSource, TResult> Sequence<TSource> .select(selector: (TSource, Int) -> TResult): Sequence<TResult>
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    ࣹӨϝιου!ͱ!ΠϯσοΫε෇͖ࣹӨϝιου ҰҙʹܾΊΒΕͳ͍͔ΒίϯύΠϧΤϥʔ sequenceOf(1, 2, 3).select { it * 2 }

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    KotLinq(Ͱ͸ɺΠϯσοΫε෇͖ࣹӨϝιουΛ ผ໊ʹ͠·ͨ͠ sequence.select { it * it }!ͱ͔͍ͨ͠͠

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    ·ͱΊ • ঢ়گʹԠͯ͡SequenceΛ࢖͏΂͖ͳ݅ • ཁૉ͕ۭͷ࣌ͷaverageϝιου͕0.0Λฦͯ͠͠·͏݅ • Ωʔ͕ॏෳͨ͠ࡍͷassociateܥϝιου͕ྫ֎Λ౤͛ͳ͍݅ • σϑΥϧτΠϯϙʔτ֦ுؔ਺Λ্ॻ͖Ͱ͖Δ݅ •

    ϝιουͷΦʔόʔϩʔυͱit͕૬ੑѱ͍݅
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    ·ͱΊ KotLinqʹ੕Λ