katzkb

// ①マップを生成
val groupMap: Map[UserId, Seq[Group]] =
  // ②マッピング数分回る
  groupMemberSeq.groupBy(_.userId) map { case (userId, members) =>
    (
      userId,
      members.flatMap(member => // ③そのユーザーのマッピング数分回る
        groupSeq.find(_.id == member.groupId) // ④Vectorのfindは実質定数
      )
    )

katzkb

val startTime = System.currentTimeMillis
val groupMap: Map[UserId, Seq[Group]] =
  groupMemberSeq.groupBy(_.userId) map { case (userId, members) =>
    (
      userId,
      members.flatMap(member =>
        groupSeq.find(_.id == member.groupId)
      )
    )
}

katzkb

val result: Seq[UserView] = userSeq.map(user => { // ①ユーザー人数分回る
  val groupIdSeq: Seq[GroupId] =
    groupMemberSeq
      .filter(_.userId == user.id) // ②マッピング数分回る
      .map(_.groupId)
val userGroups: Seq[Group] =
    groupSeq.filter(group => // ③グループ数分回る
      groupIdSeq.contains(group.id)
    )
UserView(

katzkb

// データを10,000件用意
val userSeq: Seq[User] = 
  (1L to 10000L).map(id => User(UserId(id), "name" + id.toString))
val groupSeq: Seq[Group] = 
  (1L to 10000L).map(id => Group(GroupId(id), "name" + id.toString))
val groupMemberSeq: Seq[GroupMember] = 
  (1L to 10000L).map(id => GroupMember(GroupMemberId(id), UserId(id), GroupId(id)))
...

katzkb

// データを10件用意
val userSeq: Seq[User] = 
  (1L to 10L).map(id => User(UserId(id), "name" + id.toString))
val groupSeq: Seq[Group] = 
  (1L to 10L).map(id => Group(GroupId(id), "name" + id.toString))
val groupMemberSeq: Seq[GroupMember] = 
  (1L to 10L).map(id => GroupMember(GroupMemberId(id), UserId(id), GroupId(id)))
val startTime = System.currentTimeMillis
val result: Seq[UserView] = ...
println((System.currentTimeMillis - startTime).toString + "ミリ秒")

katzkb

val userSeq: Seq[User] = UserRepository.findAll();
val groupSeq: Seq[Group] = GroupRepository.findAll();
val groupMemberSeq: Seq[GroupMember] = GroupMembersRepository.findAll();
val result: Seq[UserView] = userSeq.map(user => { // ①
  val groupIdSeq: Seq[GroupId] =
    groupMemberSeq
      .filter(_.userId == user.id) // ②
      .map(_.groupId)
val userGroups: Seq[Group] = // ③
    groupSeq.filter(group =>

katzkb

case class UserView(
  id:     UserId,
  name:   String,
  groups: Seq[Group]
)
val result: Seq[UserView] = ???

katzkb

case class UserId(value: Long)
case class User (
  id:     UserId,
  name:   String
)
case class GroupId(value: Long)
case class Group (
  id:     GroupId,
  name:   String
)

katzkb

import scala.math.abs
// 気温リスト1~12月
val temperatureSeq:Seq[Int] =
  Seq(4, 5, 11, 17, 19, 22, 28, 28, 22, 19, 14, 7)
def diffTemperature2(tSeq: Seq[Int]) = {
  tSeq.sliding(2).foldLeft(Seq.empty[Int])((totalSeq, numSeq) =>
    totalSeq :+ abs(numSeq.head - numSeq.last)
  )
}
diffTemperature2(temperatureSeq)

katzkb

import scala.math.abs
// 気温リスト1~12月
val temperatureSeq:Seq[Int] =
  Seq(4, 5, 11, 17, 19, 22, 28, 28, 22, 19, 14, 7)
def diffTemperature1(tSeq: Seq[Int]) = {
  @scala.annotation.tailrec
  def f(diffSeq:Seq[Int], tSeq: Seq[Int]): Seq[Int] = {
    tSeq match {
      case head +: second +: tail =>
        f(diffSeq :+ abs(head - second), second +: tail)