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Scala list with same adjacent values

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12

1

I have this list:

List("Black","Black","Green","White")

How can I check if a list has two adjacent values which are the same? Like so:

List("Black","Black","Green","White") true

List("Black","Yellow","Green","White") false

List("Black","Yellow","Black","Yellow") false

scala functional-programming

share|improve this question

edited May 29 at 20:00

Pika the Wizard of the Whales

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asked May 29 at 11:05

jakstackjakstack

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add a comment
 | 

12

1

I have this list:

List("Black","Black","Green","White")

How can I check if a list has two adjacent values which are the same? Like so:

List("Black","Black","Green","White") true

List("Black","Yellow","Green","White") false

List("Black","Yellow","Black","Yellow") false

scala functional-programming

share|improve this question

edited May 29 at 20:00

Pika the Wizard of the Whales

2,21688 gold badges1818 silver badges3030 bronze badges

asked May 29 at 11:05

jakstackjakstack

1,15922 gold badges1111 silver badges2626 bronze badges

add a comment
 | 

I have this list:

List("Black","Black","Green","White")

How can I check if a list has two adjacent values which are the same? Like so:

List("Black","Black","Green","White") true

List("Black","Yellow","Green","White") false

List("Black","Yellow","Black","Yellow") false

scala functional-programming

share|improve this question

edited May 29 at 20:00

Pika the Wizard of the Whales

2,21688 gold badges1818 silver badges3030 bronze badges

asked May 29 at 11:05

jakstackjakstack

1,15922 gold badges1111 silver badges2626 bronze badges

List("Black","Black","Green","White")

List("Black","Black","Green","White") true

List("Black","Yellow","Green","White") false

List("Black","Yellow","Black","Yellow") false

share|improve this question

edited May 29 at 20:00

Pika the Wizard of the Whales

2,21688 gold badges1818 silver badges3030 bronze badges

asked May 29 at 11:05

jakstackjakstack

1,15922 gold badges1111 silver badges2626 bronze badges

share|improve this question

edited May 29 at 20:00

Pika the Wizard of the Whales

2,21688 gold badges1818 silver badges3030 bronze badges

asked May 29 at 11:05

jakstackjakstack

1,15922 gold badges1111 silver badges2626 bronze badges

edited May 29 at 20:00

Pika the Wizard of the Whales

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edited May 29 at 20:00

Pika the Wizard of the Whales

2,21688 gold badges1818 silver badges3030 bronze badges

asked May 29 at 11:05

jakstackjakstack

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asked May 29 at 11:05

jakstackjakstack

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3 Answers
3

active

oldest

votes

18

In addition to Valy Dia's solution, you can also write:

list.sliding(2).exists(_.distinct.size == 1)

REPL Session

scala> def check[A](l: Seq[A]): Boolean = l.sliding(2).exists(_.distinct.size == 1)
check: [A](l: Seq[A])Boolean

scala> check("A" :: "B" :: Nil)
res0: Boolean = false

scala> check("A" :: "B" :: "B" ::Nil)
res1: Boolean = true

scala> check("A" :: "B" :: "C":: "B" ::Nil)
res2: Boolean = false

share|improve this answer

answered May 29 at 11:15

ziggystarziggystar

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8

You can try:

def check[A](l: List[A]): Boolean = 
 l.zip(l.tail).exists case (x,y) => x == y 

check(List("Black","Black","Green","White"))
//res5: Boolean = true

check(List("Black","Yellow","Green","White"))
//res6: Boolean = false

check(List("Black","Yellow","Black","Yellow"))
//res7: Boolean = false

share|improve this answer

edited May 29 at 11:22

answered May 29 at 11:12

Valy DiaValy Dia

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4

val listA = List("Black","Black","Green","White")

listA.sliding(2).mapcase a::b::_ if a == b => true else false.contains(true)

share|improve this answer

edited May 29 at 11:34

answered May 29 at 11:07

Dionysis Nt.Dionysis Nt.

74511 gold badge44 silver badges1313 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  I don´t think that is what he asked, "two adjacent values"
  
  – Pedro Correia Luís
  May 29 at 11:10
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  updated the question with another example at the end
  
  – jakstack
  May 29 at 11:10
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Your case expression is wrong - a::b binds a to the head and b to the tail so a == b is always false since you're comparing a String to a List[String]. You can replace the map/contains with exists i.e. listA.sliding(2).exists case a::b::_ => a == b .
  
  – Lee
  May 29 at 11:33
  
  

  
  
  
  

add a comment
 | 

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18

In addition to Valy Dia's solution, you can also write:

list.sliding(2).exists(_.distinct.size == 1)

REPL Session

scala> def check[A](l: Seq[A]): Boolean = l.sliding(2).exists(_.distinct.size == 1)
check: [A](l: Seq[A])Boolean

scala> check("A" :: "B" :: Nil)
res0: Boolean = false

scala> check("A" :: "B" :: "B" ::Nil)
res1: Boolean = true

scala> check("A" :: "B" :: "C":: "B" ::Nil)
res2: Boolean = false

share|improve this answer

answered May 29 at 11:15

ziggystarziggystar

20.7k88 gold badges6060 silver badges112112 bronze badges

add a comment
 | 

18

In addition to Valy Dia's solution, you can also write:

list.sliding(2).exists(_.distinct.size == 1)

REPL Session

scala> def check[A](l: Seq[A]): Boolean = l.sliding(2).exists(_.distinct.size == 1)
check: [A](l: Seq[A])Boolean

scala> check("A" :: "B" :: Nil)
res0: Boolean = false

scala> check("A" :: "B" :: "B" ::Nil)
res1: Boolean = true

scala> check("A" :: "B" :: "C":: "B" ::Nil)
res2: Boolean = false

share|improve this answer

answered May 29 at 11:15

ziggystarziggystar

20.7k88 gold badges6060 silver badges112112 bronze badges

add a comment
 | 

In addition to Valy Dia's solution, you can also write:

list.sliding(2).exists(_.distinct.size == 1)

REPL Session

scala> def check[A](l: Seq[A]): Boolean = l.sliding(2).exists(_.distinct.size == 1)
check: [A](l: Seq[A])Boolean

scala> check("A" :: "B" :: Nil)
res0: Boolean = false

scala> check("A" :: "B" :: "B" ::Nil)
res1: Boolean = true

scala> check("A" :: "B" :: "C":: "B" ::Nil)
res2: Boolean = false

share|improve this answer

answered May 29 at 11:15

ziggystarziggystar

20.7k88 gold badges6060 silver badges112112 bronze badges

list.sliding(2).exists(_.distinct.size == 1)

scala> def check[A](l: Seq[A]): Boolean = l.sliding(2).exists(_.distinct.size == 1)
check: [A](l: Seq[A])Boolean

scala> check("A" :: "B" :: Nil)
res0: Boolean = false

scala> check("A" :: "B" :: "B" ::Nil)
res1: Boolean = true

scala> check("A" :: "B" :: "C":: "B" ::Nil)
res2: Boolean = false

share|improve this answer

answered May 29 at 11:15

ziggystarziggystar

20.7k88 gold badges6060 silver badges112112 bronze badges

answered May 29 at 11:15

ziggystarziggystar

20.7k88 gold badges6060 silver badges112112 bronze badges

answered May 29 at 11:15

ziggystarziggystar

20.7k88 gold badges6060 silver badges112112 bronze badges

8

You can try:

def check[A](l: List[A]): Boolean = 
 l.zip(l.tail).exists case (x,y) => x == y 

check(List("Black","Black","Green","White"))
//res5: Boolean = true

check(List("Black","Yellow","Green","White"))
//res6: Boolean = false

check(List("Black","Yellow","Black","Yellow"))
//res7: Boolean = false

share|improve this answer

edited May 29 at 11:22

answered May 29 at 11:12

Valy DiaValy Dia

2,16122 gold badges77 silver badges2424 bronze badges

add a comment
 | 

8

You can try:

def check[A](l: List[A]): Boolean = 
 l.zip(l.tail).exists case (x,y) => x == y 

check(List("Black","Black","Green","White"))
//res5: Boolean = true

check(List("Black","Yellow","Green","White"))
//res6: Boolean = false

check(List("Black","Yellow","Black","Yellow"))
//res7: Boolean = false

share|improve this answer

edited May 29 at 11:22

answered May 29 at 11:12

Valy DiaValy Dia

2,16122 gold badges77 silver badges2424 bronze badges

add a comment
 | 

You can try:

def check[A](l: List[A]): Boolean = 
 l.zip(l.tail).exists case (x,y) => x == y 

check(List("Black","Black","Green","White"))
//res5: Boolean = true

check(List("Black","Yellow","Green","White"))
//res6: Boolean = false

check(List("Black","Yellow","Black","Yellow"))
//res7: Boolean = false

share|improve this answer

edited May 29 at 11:22

answered May 29 at 11:12

Valy DiaValy Dia

2,16122 gold badges77 silver badges2424 bronze badges

def check[A](l: List[A]): Boolean = 
 l.zip(l.tail).exists case (x,y) => x == y 

check(List("Black","Black","Green","White"))
//res5: Boolean = true

check(List("Black","Yellow","Green","White"))
//res6: Boolean = false

check(List("Black","Yellow","Black","Yellow"))
//res7: Boolean = false

share|improve this answer

edited May 29 at 11:22

answered May 29 at 11:12

Valy DiaValy Dia

2,16122 gold badges77 silver badges2424 bronze badges

answered May 29 at 11:12

Valy DiaValy Dia

2,16122 gold badges77 silver badges2424 bronze badges

answered May 29 at 11:12

Valy DiaValy Dia

2,16122 gold badges77 silver badges2424 bronze badges

4

val listA = List("Black","Black","Green","White")

listA.sliding(2).mapcase a::b::_ if a == b => true else false.contains(true)

share|improve this answer

edited May 29 at 11:34

answered May 29 at 11:07

Dionysis Nt.Dionysis Nt.

74511 gold badge44 silver badges1313 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  I don´t think that is what he asked, "two adjacent values"
  
  – Pedro Correia Luís
  May 29 at 11:10
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  updated the question with another example at the end
  
  – jakstack
  May 29 at 11:10
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Your case expression is wrong - a::b binds a to the head and b to the tail so a == b is always false since you're comparing a String to a List[String]. You can replace the map/contains with exists i.e. listA.sliding(2).exists case a::b::_ => a == b .
  
  – Lee
  May 29 at 11:33
  
  

  
  
  
  

add a comment
 | 

4

val listA = List("Black","Black","Green","White")

listA.sliding(2).mapcase a::b::_ if a == b => true else false.contains(true)

share|improve this answer

edited May 29 at 11:34

answered May 29 at 11:07

Dionysis Nt.Dionysis Nt.

74511 gold badge44 silver badges1313 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  I don´t think that is what he asked, "two adjacent values"
  
  – Pedro Correia Luís
  May 29 at 11:10
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  updated the question with another example at the end
  
  – jakstack
  May 29 at 11:10
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Your case expression is wrong - a::b binds a to the head and b to the tail so a == b is always false since you're comparing a String to a List[String]. You can replace the map/contains with exists i.e. listA.sliding(2).exists case a::b::_ => a == b .
  
  – Lee
  May 29 at 11:33
  
  

  
  
  
  

add a comment
 | 

val listA = List("Black","Black","Green","White")

listA.sliding(2).mapcase a::b::_ if a == b => true else false.contains(true)

share|improve this answer

edited May 29 at 11:34

answered May 29 at 11:07

Dionysis Nt.Dionysis Nt.

74511 gold badge44 silver badges1313 bronze badges

val listA = List("Black","Black","Green","White")

listA.sliding(2).mapcase a::b::_ if a == b => true else false.contains(true)

share|improve this answer

edited May 29 at 11:34

answered May 29 at 11:07

Dionysis Nt.Dionysis Nt.

74511 gold badge44 silver badges1313 bronze badges

answered May 29 at 11:07

Dionysis Nt.Dionysis Nt.

74511 gold badge44 silver badges1313 bronze badges

answered May 29 at 11:07

Dionysis Nt.Dionysis Nt.

74511 gold badge44 silver badges1313 bronze badges