create a map from list in Scala

Question

I need to create a HashMap of directory-to-file in scala while I list all files in the directory. How can I achieve this in scala?

val directoryToFile = awsClient.listFiles(uploadPath).collect {
  case path if !path.endsWith("/") => {
    path match {
      // do some regex matching to get directory & file names
      case regex(dir, date) => {
          // NEED TO CREATE A HASH MAP OF dir -> date. How???
      }
      case _ => None
    }
  }
}

The method listFiles(path: String) returns a Seq[String] of absolute path of all files in the path passed as argument to the function

@YuvalItzchakov Seq[String] which is a list of absolute paths for all files in the directory — Darth.Vader
– Darth.Vader, Commented Nov 6, 2016 at 15:26

Rok Kralj · Accepted Answer · 2016-11-06 16:00:22Z

0

Try to write more idiomatic Scala. Something like this:

val directoryToFile = (for {
    path <- awsClient.listFiles(uploadPath)
    if !path.endsWith("/")
    regex(dir, date) <- regex.findFirstIn(path)
} yield dir -> date).sortBy(_._2).toMap

edited Nov 6, 2016 at 16:00

answered Nov 6, 2016 at 15:49

Rok Kralj

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2 Comments

Victor Moroz Over a year ago

What sortBy is for? Map in Scala is unordered.

Rok Kralj Over a year ago

You said you wanted only the last (most recent) date associated with each dir. This is the purpose of the sortBy statement. You can also remove that, if you do not need it.

Yuval Itzchakov · Accepted Answer · 2016-11-06 17:32:00Z

0

You can filter and then foldLeft:

val l = List("""/opt/file1.txt""", """/opt/file2.txt""")
val finalMap = l
                .filter(!_.endsWith("/"))
                .foldLeft(Map.empty[String, LocalDateTime])((map, s) =>
  s match {
    case regex(dir, date) => map + (dir -> date)
    case _ => map
  }
)

edited Nov 6, 2016 at 17:32

answered Nov 6, 2016 at 15:33

Yuval Itzchakov

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6 Comments

Darth.Vader Over a year ago

thanks! What about the "collect" method where I was filtering out some elements based on a certain criteria in the original code?

Yuval Itzchakov Over a year ago

You can apply a filter before using foldLeft. Edited the answer.

Darth.Vader Over a year ago

thank you! Now, I minor update: there could be a situation that the same directory may have multiple files denoted by date: "dir1/2016-01-01.txt" and "dir1/2013-01-01/txt". In that case, I want the hashmap to only keep the value with the latest file date.. how can I use "max" function to do that?

Yuval Itzchakov Over a year ago

+ on immutable.Map with the same key will override the previous entry.

Rok Kralj Over a year ago

See my solutions. I have added your "max" function.

|

Victor Moroz · Accepted Answer · 2016-11-06 17:37:14Z

-1

You can try something like this:

val regex =  """(\d)-(\d)""".r
val paths = List("1-2", "3-4", "555")

for {

  // Hint to Scala to produce specific type
  _ <- Map("" -> "")

  // Not sure why your !path.endsWith("/") is not part of regex
  path@regex(a, b) <- paths
  if path.startsWith("1")

} yield (a, b)

//> scala.collection.immutable.Map[String,String] = Map(1 -> 2)

Slightly more complicated if you need max:

val regex =  """(\d)-(\d)""".r
val paths = List("1-2", "3-4", "555", "1-3")

for {
  (_, ps) <-
    ( for {
        path@regex(a, b) <- paths
        if path.startsWith("1")
      } yield (a, b)
    ).groupBy(_._1)
} yield ps.maxBy(_._2)

//> scala.collection.immutable.Map[String,String] = Map(1 -> 3)

edited Nov 6, 2016 at 17:37

answered Nov 6, 2016 at 17:05

Victor Moroz

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