How to create an immutable Map in Scala using foldings?

-4

I am trying to create an immutable hash Map[String, (String, Int)] using the following code:

def genList(xx: String) = {

    Seq("one", "two", "three", "four")

}



val oriwords = Set("hello", "how", "are", "you")



val newMap = (Map[String, (String, Int)]() /: oriwords) (

    (cmap, currentWord) => {

        val xv = 2



        genList(currentWord).map(ps => {

            val src = cmap get ps



            if(src == None) {

                cmap + (ps -> ((currentWord, xv)))

            }

            else {

                if(src.get._2 < xv) {

                    cmap + (ps -> ((currentWord, xv)))

                }

                else cmap

            }



        })

    }

)

With this code I am getting the following exception:

error: type mismatch;

 found   : Seq[scala.collection.immutable.Map[String,(String, Int)]]

 required: scala.collection.immutable.Map[String,(String, Int)]

               genList(currentWord).map(ps => {

                                       ^

I know that it is returning a list of Map[String, (String, Int)] as opposed to an update for Map[String, (String, Int)] for the fold operation. Unfortunately,
I am getting any pointers how to fix it. I am very new to Scala.

Expected output is:

scala.collection.immutable.Map[String,(String, Int)] = Map(one -> (are,2), two -> (are,2), three -> (are,2), four -> (are,2))

edited Nov 19 '18 at 22:42

halfer

14.4k758109

asked Nov 19 '18 at 9:03

user3243499

75611126

Can you provide an example of what your output should look like?

– Terry Dactyl
Nov 19 '18 at 9:29

Output should be a map[String, (String, Int)]. For example, in this case it would be, scala.collection.immutable.Map[String,(String, Int)] = Map(one -> (are,2), two -> (are,2), three -> (are,2), four -> (are,2))

– user3243499
Nov 19 '18 at 9:34

updated description as well as comment.

– user3243499
Nov 19 '18 at 9:35

One way to fix the error is to change the map() call to a fold, but you still might not get the output you're looking for. oriwords is a Set and sets have no defined order, so the order of elements that appear in the fold operation is indeterminate and probably not the order you expect.

– jwvh
Nov 19 '18 at 9:48

Order is not of concerned. I only intend to get the hash map of key value pairs.

– user3243499
Nov 19 '18 at 10:21

|
show 2 more comments

-4

I am trying to create an immutable hash Map[String, (String, Int)] using the following code:

def genList(xx: String) = {

    Seq("one", "two", "three", "four")

}



val oriwords = Set("hello", "how", "are", "you")



val newMap = (Map[String, (String, Int)]() /: oriwords) (

    (cmap, currentWord) => {

        val xv = 2



        genList(currentWord).map(ps => {

            val src = cmap get ps



            if(src == None) {

                cmap + (ps -> ((currentWord, xv)))

            }

            else {

                if(src.get._2 < xv) {

                    cmap + (ps -> ((currentWord, xv)))

                }

                else cmap

            }



        })

    }

)

With this code I am getting the following exception:

error: type mismatch;

 found   : Seq[scala.collection.immutable.Map[String,(String, Int)]]

 required: scala.collection.immutable.Map[String,(String, Int)]

               genList(currentWord).map(ps => {

                                       ^

Expected output is:

scala.collection.immutable.Map[String,(String, Int)] = Map(one -> (are,2), two -> (are,2), three -> (are,2), four -> (are,2))

edited Nov 19 '18 at 22:42

halfer

14.4k758109

asked Nov 19 '18 at 9:03

user3243499

75611126

Can you provide an example of what your output should look like?

– Terry Dactyl
Nov 19 '18 at 9:29

Output should be a map[String, (String, Int)]. For example, in this case it would be, scala.collection.immutable.Map[String,(String, Int)] = Map(one -> (are,2), two -> (are,2), three -> (are,2), four -> (are,2))

– user3243499
Nov 19 '18 at 9:34

updated description as well as comment.

– user3243499
Nov 19 '18 at 9:35

One way to fix the error is to change the map() call to a fold, but you still might not get the output you're looking for. oriwords is a Set and sets have no defined order, so the order of elements that appear in the fold operation is indeterminate and probably not the order you expect.

– jwvh
Nov 19 '18 at 9:48

Order is not of concerned. I only intend to get the hash map of key value pairs.

– user3243499
Nov 19 '18 at 10:21

|
show 2 more comments

-4

I am trying to create an immutable hash Map[String, (String, Int)] using the following code:

def genList(xx: String) = {

    Seq("one", "two", "three", "four")

}



val oriwords = Set("hello", "how", "are", "you")



val newMap = (Map[String, (String, Int)]() /: oriwords) (

    (cmap, currentWord) => {

        val xv = 2



        genList(currentWord).map(ps => {

            val src = cmap get ps



            if(src == None) {

                cmap + (ps -> ((currentWord, xv)))

            }

            else {

                if(src.get._2 < xv) {

                    cmap + (ps -> ((currentWord, xv)))

                }

                else cmap

            }



        })

    }

)

With this code I am getting the following exception:

error: type mismatch;

 found   : Seq[scala.collection.immutable.Map[String,(String, Int)]]

 required: scala.collection.immutable.Map[String,(String, Int)]

               genList(currentWord).map(ps => {

                                       ^

Expected output is:

scala.collection.immutable.Map[String,(String, Int)] = Map(one -> (are,2), two -> (are,2), three -> (are,2), four -> (are,2))

edited Nov 19 '18 at 22:42

halfer

14.4k758109

asked Nov 19 '18 at 9:03

user3243499

75611126

I am trying to create an immutable hash Map[String, (String, Int)] using the following code:

def genList(xx: String) = {

    Seq("one", "two", "three", "four")

}



val oriwords = Set("hello", "how", "are", "you")



val newMap = (Map[String, (String, Int)]() /: oriwords) (

    (cmap, currentWord) => {

        val xv = 2



        genList(currentWord).map(ps => {

            val src = cmap get ps



            if(src == None) {

                cmap + (ps -> ((currentWord, xv)))

            }

            else {

                if(src.get._2 < xv) {

                    cmap + (ps -> ((currentWord, xv)))

                }

                else cmap

            }



        })

    }

)

With this code I am getting the following exception:

error: type mismatch;

 found   : Seq[scala.collection.immutable.Map[String,(String, Int)]]

 required: scala.collection.immutable.Map[String,(String, Int)]

               genList(currentWord).map(ps => {

                                       ^

Expected output is:

scala.collection.immutable.Map[String,(String, Int)] = Map(one -> (are,2), two -> (are,2), three -> (are,2), four -> (are,2))

scala

edited Nov 19 '18 at 22:42

halfer

14.4k758109

asked Nov 19 '18 at 9:03

user3243499

75611126

edited Nov 19 '18 at 22:42

halfer

14.4k758109

asked Nov 19 '18 at 9:03

user3243499

75611126

edited Nov 19 '18 at 22:42

halfer

14.4k758109

edited Nov 19 '18 at 22:42

halfer

14.4k758109

edited Nov 19 '18 at 22:42

halfer

14.4k758109

asked Nov 19 '18 at 9:03

user3243499

75611126

asked Nov 19 '18 at 9:03

user3243499

75611126

asked Nov 19 '18 at 9:03

user3243499

75611126

Can you provide an example of what your output should look like?

– Terry Dactyl
Nov 19 '18 at 9:29

Output should be a map[String, (String, Int)]. For example, in this case it would be, scala.collection.immutable.Map[String,(String, Int)] = Map(one -> (are,2), two -> (are,2), three -> (are,2), four -> (are,2))

– user3243499
Nov 19 '18 at 9:34

updated description as well as comment.

– user3243499
Nov 19 '18 at 9:35

One way to fix the error is to change the map() call to a fold, but you still might not get the output you're looking for. oriwords is a Set and sets have no defined order, so the order of elements that appear in the fold operation is indeterminate and probably not the order you expect.

– jwvh
Nov 19 '18 at 9:48

Order is not of concerned. I only intend to get the hash map of key value pairs.

– user3243499
Nov 19 '18 at 10:21

|
show 2 more comments

Can you provide an example of what your output should look like?

– Terry Dactyl
Nov 19 '18 at 9:29

Output should be a map[String, (String, Int)]. For example, in this case it would be, scala.collection.immutable.Map[String,(String, Int)] = Map(one -> (are,2), two -> (are,2), three -> (are,2), four -> (are,2))

– user3243499
Nov 19 '18 at 9:34

updated description as well as comment.

– user3243499
Nov 19 '18 at 9:35

One way to fix the error is to change the map() call to a fold, but you still might not get the output you're looking for. oriwords is a Set and sets have no defined order, so the order of elements that appear in the fold operation is indeterminate and probably not the order you expect.

– jwvh
Nov 19 '18 at 9:48

Order is not of concerned. I only intend to get the hash map of key value pairs.

– user3243499
Nov 19 '18 at 10:21

Can you provide an example of what your output should look like?

– Terry Dactyl
Nov 19 '18 at 9:29

Output should be a map[String, (String, Int)]. For example, in this case it would be,

scala.collection.immutable.Map[String,(String, Int)] = Map(one -> (are,2), two -> (are,2), three -> (are,2), four -> (are,2))

– user3243499
Nov 19 '18 at 9:34

Output should be a map[String, (String, Int)]. For example, in this case it would be,

scala.collection.immutable.Map[String,(String, Int)] = Map(one -> (are,2), two -> (are,2), three -> (are,2), four -> (are,2))

– user3243499
Nov 19 '18 at 9:34

updated description as well as comment.

– user3243499
Nov 19 '18 at 9:35

One way to fix the error is to change the map() call to a fold, but you still might not get the output you're looking for. oriwords is a Set and sets have no defined order, so the order of elements that appear in the fold operation is indeterminate and probably not the order you expect.

– jwvh
Nov 19 '18 at 9:48

Order is not of concerned. I only intend to get the hash map of key value pairs.

– user3243499
Nov 19 '18 at 10:21

|
show 2 more comments

2 Answers
2

active

oldest

votes

Using fold:

def genList(xx: String) = {

    Seq("one", "two", "three", "four")

}



val oriwords = Set("hello", "how", "are", "you")



val newMap = (Map[String, (String, Int)]() /: oriwords) (

    (cmap, currentWord) => {

        val xv = 2



        genList(currentWord).map(ps => {

            val src = cmap get ps



            if(src == None) {

                cmap + (ps -> ((currentWord, xv)))

            }

            else {

                if(src.get._2 < xv) {

                    cmap + (ps -> ((currentWord, xv)))

                }

                else cmap

            }



        }).fold(Map[String, (String, Int)]())((a, b) => a ++ b)

    }

)

println(newMap) //Map(one -> (hello,2), two -> (hello,2), three -> (hello,2), four -> (hello,2))

edited Nov 19 '18 at 10:06

answered Nov 19 '18 at 9:51

Raman Mishra

1,2741417

add a comment |

The accumulator your foldLeft returns is of type Seq[Map[String, (String, Int)]] when it should be Map[String, (String, Int)]

As mentioned above the reason is because you are calling map on a Seq which returns a Seq. You can solve the problem by using foldLeft

  def genList(xx: String) = {

    Seq("one", "two", "three", "four")

  }



  val oriwords = Set("hello", "how", "are", "you")



  val newMap = (Map[String, (String, Int)]() /: oriwords) (

    (cmap, currentWord) => {

      val xv = 2



      genList(currentWord).foldLeft(cmap) {

        (acc, ps) => {

          val src = acc get ps



          if (src == None) {

            acc + (ps -> ((currentWord, xv)))

          }

          else {

            if (src.get._2 < xv) {

              acc + (ps -> ((currentWord, xv)))

            }

            else acc

          }



        }

      }

    }

  )



  println(newMap)



Map(one -> (hello,2), two -> (hello,2), three -> (hello,2), four -> (hello,2))

However the output does not match the expected values so you will need to check your logic...

edited Nov 19 '18 at 10:25

answered Nov 19 '18 at 9:59

Terry Dactyl

1,104412

add a comment |

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

Using fold:

def genList(xx: String) = {

    Seq("one", "two", "three", "four")

}



val oriwords = Set("hello", "how", "are", "you")



val newMap = (Map[String, (String, Int)]() /: oriwords) (

    (cmap, currentWord) => {

        val xv = 2



        genList(currentWord).map(ps => {

            val src = cmap get ps



            if(src == None) {

                cmap + (ps -> ((currentWord, xv)))

            }

            else {

                if(src.get._2 < xv) {

                    cmap + (ps -> ((currentWord, xv)))

                }

                else cmap

            }



        }).fold(Map[String, (String, Int)]())((a, b) => a ++ b)

    }

)

println(newMap) //Map(one -> (hello,2), two -> (hello,2), three -> (hello,2), four -> (hello,2))

edited Nov 19 '18 at 10:06

answered Nov 19 '18 at 9:51

Raman Mishra

1,2741417

add a comment |

Using fold:

def genList(xx: String) = {

    Seq("one", "two", "three", "four")

}



val oriwords = Set("hello", "how", "are", "you")



val newMap = (Map[String, (String, Int)]() /: oriwords) (

    (cmap, currentWord) => {

        val xv = 2



        genList(currentWord).map(ps => {

            val src = cmap get ps



            if(src == None) {

                cmap + (ps -> ((currentWord, xv)))

            }

            else {

                if(src.get._2 < xv) {

                    cmap + (ps -> ((currentWord, xv)))

                }

                else cmap

            }



        }).fold(Map[String, (String, Int)]())((a, b) => a ++ b)

    }

)

println(newMap) //Map(one -> (hello,2), two -> (hello,2), three -> (hello,2), four -> (hello,2))

edited Nov 19 '18 at 10:06

answered Nov 19 '18 at 9:51

Raman Mishra

1,2741417

add a comment |

Using fold:

def genList(xx: String) = {

    Seq("one", "two", "three", "four")

}



val oriwords = Set("hello", "how", "are", "you")



val newMap = (Map[String, (String, Int)]() /: oriwords) (

    (cmap, currentWord) => {

        val xv = 2



        genList(currentWord).map(ps => {

            val src = cmap get ps



            if(src == None) {

                cmap + (ps -> ((currentWord, xv)))

            }

            else {

                if(src.get._2 < xv) {

                    cmap + (ps -> ((currentWord, xv)))

                }

                else cmap

            }



        }).fold(Map[String, (String, Int)]())((a, b) => a ++ b)

    }

)

println(newMap) //Map(one -> (hello,2), two -> (hello,2), three -> (hello,2), four -> (hello,2))

edited Nov 19 '18 at 10:06

answered Nov 19 '18 at 9:51

Raman Mishra

1,2741417

Using fold:

def genList(xx: String) = {

    Seq("one", "two", "three", "four")

}



val oriwords = Set("hello", "how", "are", "you")



val newMap = (Map[String, (String, Int)]() /: oriwords) (

    (cmap, currentWord) => {

        val xv = 2



        genList(currentWord).map(ps => {

            val src = cmap get ps



            if(src == None) {

                cmap + (ps -> ((currentWord, xv)))

            }

            else {

                if(src.get._2 < xv) {

                    cmap + (ps -> ((currentWord, xv)))

                }

                else cmap

            }



        }).fold(Map[String, (String, Int)]())((a, b) => a ++ b)

    }

)

println(newMap) //Map(one -> (hello,2), two -> (hello,2), three -> (hello,2), four -> (hello,2))

edited Nov 19 '18 at 10:06

answered Nov 19 '18 at 9:51

Raman Mishra

1,2741417

edited Nov 19 '18 at 10:06

answered Nov 19 '18 at 9:51

Raman Mishra

1,2741417

answered Nov 19 '18 at 9:51

Raman Mishra

1,2741417

answered Nov 19 '18 at 9:51

Raman Mishra

1,2741417

add a comment |

The accumulator your foldLeft returns is of type Seq[Map[String, (String, Int)]] when it should be Map[String, (String, Int)]

As mentioned above the reason is because you are calling map on a Seq which returns a Seq. You can solve the problem by using foldLeft

  def genList(xx: String) = {

    Seq("one", "two", "three", "four")

  }



  val oriwords = Set("hello", "how", "are", "you")



  val newMap = (Map[String, (String, Int)]() /: oriwords) (

    (cmap, currentWord) => {

      val xv = 2



      genList(currentWord).foldLeft(cmap) {

        (acc, ps) => {

          val src = acc get ps



          if (src == None) {

            acc + (ps -> ((currentWord, xv)))

          }

          else {

            if (src.get._2 < xv) {

              acc + (ps -> ((currentWord, xv)))

            }

            else acc

          }



        }

      }

    }

  )



  println(newMap)



Map(one -> (hello,2), two -> (hello,2), three -> (hello,2), four -> (hello,2))

However the output does not match the expected values so you will need to check your logic...

edited Nov 19 '18 at 10:25

answered Nov 19 '18 at 9:59

Terry Dactyl

1,104412

add a comment |

The accumulator your foldLeft returns is of type Seq[Map[String, (String, Int)]] when it should be Map[String, (String, Int)]

As mentioned above the reason is because you are calling map on a Seq which returns a Seq. You can solve the problem by using foldLeft

  def genList(xx: String) = {

    Seq("one", "two", "three", "four")

  }



  val oriwords = Set("hello", "how", "are", "you")



  val newMap = (Map[String, (String, Int)]() /: oriwords) (

    (cmap, currentWord) => {

      val xv = 2



      genList(currentWord).foldLeft(cmap) {

        (acc, ps) => {

          val src = acc get ps



          if (src == None) {

            acc + (ps -> ((currentWord, xv)))

          }

          else {

            if (src.get._2 < xv) {

              acc + (ps -> ((currentWord, xv)))

            }

            else acc

          }



        }

      }

    }

  )



  println(newMap)



Map(one -> (hello,2), two -> (hello,2), three -> (hello,2), four -> (hello,2))

However the output does not match the expected values so you will need to check your logic...

edited Nov 19 '18 at 10:25

answered Nov 19 '18 at 9:59

Terry Dactyl

1,104412

add a comment |

The accumulator your foldLeft returns is of type Seq[Map[String, (String, Int)]] when it should be Map[String, (String, Int)]

As mentioned above the reason is because you are calling map on a Seq which returns a Seq. You can solve the problem by using foldLeft

  def genList(xx: String) = {

    Seq("one", "two", "three", "four")

  }



  val oriwords = Set("hello", "how", "are", "you")



  val newMap = (Map[String, (String, Int)]() /: oriwords) (

    (cmap, currentWord) => {

      val xv = 2



      genList(currentWord).foldLeft(cmap) {

        (acc, ps) => {

          val src = acc get ps



          if (src == None) {

            acc + (ps -> ((currentWord, xv)))

          }

          else {

            if (src.get._2 < xv) {

              acc + (ps -> ((currentWord, xv)))

            }

            else acc

          }



        }

      }

    }

  )



  println(newMap)



Map(one -> (hello,2), two -> (hello,2), three -> (hello,2), four -> (hello,2))

However the output does not match the expected values so you will need to check your logic...

edited Nov 19 '18 at 10:25

answered Nov 19 '18 at 9:59

Terry Dactyl

1,104412

The accumulator your foldLeft returns is of type Seq[Map[String, (String, Int)]] when it should be Map[String, (String, Int)]

As mentioned above the reason is because you are calling map on a Seq which returns a Seq. You can solve the problem by using foldLeft

  def genList(xx: String) = {

    Seq("one", "two", "three", "four")

  }



  val oriwords = Set("hello", "how", "are", "you")



  val newMap = (Map[String, (String, Int)]() /: oriwords) (

    (cmap, currentWord) => {

      val xv = 2



      genList(currentWord).foldLeft(cmap) {

        (acc, ps) => {

          val src = acc get ps



          if (src == None) {

            acc + (ps -> ((currentWord, xv)))

          }

          else {

            if (src.get._2 < xv) {

              acc + (ps -> ((currentWord, xv)))

            }

            else acc

          }



        }

      }

    }

  )



  println(newMap)



Map(one -> (hello,2), two -> (hello,2), three -> (hello,2), four -> (hello,2))

However the output does not match the expected values so you will need to check your logic...

edited Nov 19 '18 at 10:25

answered Nov 19 '18 at 9:59

Terry Dactyl

1,104412

edited Nov 19 '18 at 10:25

answered Nov 19 '18 at 9:59

Terry Dactyl

1,104412

answered Nov 19 '18 at 9:59

Terry Dactyl

1,104412

answered Nov 19 '18 at 9:59

Terry Dactyl

1,104412

add a comment |

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