hoge.scala

val file = Source.fromFile(args(0), "utf-8")
val lines = file.getLines

val dateTimeSep = """- (\d\d\d\d)年(\d\d)月(\d\d)日 .曜日 (\d\d:\d\d)""".r

val articles = mutable.TreeMap[String, String]()
var nowDate = "";
for (line <- lines) {
  line match {
    case dateTimeSep(year, month, day, time) =>
      nowDate = s"$year-$month-$day $time"
    case _ =>
      if (articles contains nowDate) {
        articles(nowDate) += line + "\n"
      } else {
        articles += (nowDate -> (line + "\n"))
      }
  }
}