How to calculate length of string in a tuple in scala - scala

Question

Given a list of tuples, where the 1st element of the tuple is an integer and the second element is a string,
scala> val tuple2 : List[(Int,String)] = List((1,"apple"),(2,"ball"),(3,"cat"),(4,"doll"),(5,"eggs"))
tuple2: List[(Int, String)] = List((1,apple), (2,ball), (3,cat), (4,doll), (5,eggs))
I want to print the numbers where the corresponding string length is 4.
Can this be done in one line ?

Answer 1

you need .collect which is filter+map
given your input,
scala> val input : List[(Int,String)] = List((1,"apple"),(2,"ball"),(3,"cat"),(4,"doll"),(5,"eggs"))
input: List[(Int, String)] = List((1,apple), (2,ball), (3,cat), (4,doll), (5,eggs))
filter those of length 4,
scala> input.collect { case(number, string) if string.length == 4 => number}
res2: List[Int] = List(2, 4, 5)
alternative solution using filter + map,
scala> input.filter { case(number, string) => string.length == 4 }
.map { case (number, string) => number}
res4: List[Int] = List(2, 4, 5)

Answer 2

you filter and print as below
tuple2.filter(_._2.length == 4).foreach(x => println(x._1))
You should have output as
2
4
5

Answer 3

I like #prayagupd answer using collect. But foldLeft is the one of my favourite function in Scala! you can use foldLeft:
scala> val input : List[(Int,String)] = List((1,"apple"),(2,"ball"),(3,"cat"),(4,"doll"),(5,"eggs"))
input: List[(Int, String)] = List((1,apple), (2,ball), (3,cat), (4,doll), (5,eggs))
scala> input.foldLeft(List.empty[Int]){case (acc, (n,str)) => if(str.length ==4) acc :+ n else acc}
res3: List[Int] = List(2, 4, 5)

Answer 4

Using a for comprehension as follows,
for ((i,s) <- tuple2 if s.size == 4) yield i
which for the example above delivers
List(2, 4, 5)
Note we pattern match and extract the elements in each tuple and filter by string size. To print a list consider for instance aList.foreach(println).

Answer 5

This will do:
tuple2.filter(_._2.size==4).map(_._1)
In Scala REPL:
scala> val tuple2 : List[(Int,String)] = List((1,"apple"),(2,"ball"),(3,"cat"),(4,"doll"),(5,"eggs"))
tuple2: List[(Int, String)] = List((1,apple), (2,ball), (3,cat), (4,doll), (5,eggs))
scala> tuple2.filter(_._2.size==4).map(_._1)
res261: List[Int] = List(2, 4, 5)
scala>