How to remove duplicates From an Array in Scala

Question

I am new to scala How can I remove Duplicates from an array. without using Distict keyword.

I have Array Like this

Input 

Array(1,2,3,1,3)
=====================

I need output like This

OutPut
====================
Array(1,2,3)

My code is

Val ar=Array(1,2,3,4,5)
for(i<-0  to ar.length-1){
if(ar(i)!=for())..?

I want to write a program without using Set And List

val dup =ar.foldLeft(Array[Int]()){(a,b)=>if(a contains(b)) a else a :+ b}

I got this solution but how it works

can any one please explain how background it works I tried

1,2,3,1,2
1==2 false .. else 1 :

duplicate of In Scala how do I remove duplicates from a list? — prayagupadhyay
– prayagupadhyay, Commented Jun 25, 2017 at 6:06
Possible duplicate of How to create a collection of unique values based on existing array values — Zernike
– Zernike, Commented Jun 25, 2017 at 6:09

Stephen · Accepted Answer · 2017-06-25 06:06:53Z

2

It seems a bit arbitrary to not want to use .distinct. But you could always turn it into a set and back.

Array(1,2,3,1,3).toSet.toArray 
res2: Array[Int] = Array(1, 2, 3)

answered Jun 25, 2017 at 6:06

Stephen

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2 Comments

Ravi Over a year ago

Nope I know this Way But I need core

Ravi Over a year ago

Without using Set and GroupBy without using Methods and Set and List

jwvh · Accepted Answer · 2017-06-25 06:36:56Z

1

Here's a very inefficient algorithm. It doesn't use distinct, Set, or groupBy.

Array(1,2,3,1,3).foldLeft(Array[Int]()){ (acc,elem) =>
  if (acc.contains(elem)) acc else acc :+ elem
}

answered Jun 25, 2017 at 6:36

jwvh

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3 Comments

Ravi Over a year ago

Thanks Its Working

Ravi Over a year ago

what does :+ do here

jwvh Over a year ago

acc :+ elem creates a copy of acc with the element elem appended.

Akavall · Accepted Answer · 2020-01-17 14:56:41Z

1

If you are OK with having your unique Array in sorted order, you can sort your original array, and only keep elements that are not equal to their neighbors:

object MyOjbect {

def makeUnique(a: Array[Int]): Array[Int] = { 
    if (a.isEmpty) return Array()

    a.head +: a.sorted.sliding(2).foldLeft(Array[Int]()) { (acc, ele) =>
                   if (ele(0) != ele(1)) acc :+ ele(1) else acc 
                   }
}   

def main(args: Array[String]) {

    println(makeUnique(Array(1,2,3,1,3)).toList) 
    println(makeUnique(Array(1,1,1,1,1)).toList)
    println(makeUnique(Array()).toList)
    }
}

Result:

List(1, 2, 3)
List(1)
List()

edited Jan 17, 2020 at 14:56

answered Jun 25, 2017 at 22:00

Akavall

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5 Comments

Ravi Over a year ago

What :+ will do

Ravi Over a year ago

what does :+ do exactly

Akavall Over a year ago

@Ravi, :+ creates a new Array, for example: val b = Array(1,2,3) :+ 4 will create a new Array b, whose contents are: Array(1, 2, 3, 4).

Ravi Over a year ago

But I have used for List as well ya its working val l=List(1,2,3,1,2).foldLeft(List[Int]()){(a,b)=>if(a contains(b)) a else a :+ b}.foreach(println(_))

Akavall Over a year ago

@Ravi, Yes, :+ is a method on scala collections (Array, List, Seq, Vector maybe more), so it works on all of them; it creates a new collection including a new variable, like in example I gave above.

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