Add element to specific index of list

Question

What is the best way of adding to a specific index of a list in scala?

This is what I have tried:

case class Level(price: Double) 

case class Order(levels: Seq[Level] = Seq())

def process(order: Order) {
    orderBook.levels.updated(0, Level(0.0))
}

I was hoping to insert into position zero the new Level but it just throws java.lang.IndexOutOfBoundsException: 0 . What is the best way of handling this? Is there a better data type other than Seq which should be used for keeping track of indexes in a list?

stackoverflow.com/questions/31037384/…

jrook
– jrook

2017-11-26 11:57:25 +00:00
Commented Nov 26, 2017 at 11:57 — jrook
– jrook, Commented Nov 26, 2017 at 11:57

Yuval Itzchakov · Accepted Answer · 2017-11-26 11:57:30Z

2

Is there a better data type other than Seq which should be used for keeping track of indexes in a list?

Yes, a Vector[T] is recommended when you want random access into the underlying collection:

scala> val vector = Vector(1,2,3)
vector: scala.collection.immutable.Vector[Int] = Vector(1, 2, 3)

scala> vector.updated(0, 5)
res3: scala.collection.immutable.Vector[Int] = Vector(5, 2, 3)

Note that a Vector will also through an IndexOutOfBoundsException when you try to insert data into an empty vector. A good way of appending and prepending data is using :+ and :+, respectively:

scala> val vec = Vector[Int]()
vec: scala.collection.immutable.Vector[Int] = Vector()

scala> vec :+ 1 :+ 2
res7: scala.collection.immutable.Vector[Int] = Vector(1, 2)

answered Nov 26, 2017 at 11:57

Yuval Itzchakov

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2 Comments

maloney Over a year ago

Thanks! How do you use the newly updated Vector to overwrite the existing one stored in Order? How about if you want to insert (not update) into the Vector?

Yuval Itzchakov Over a year ago

@maloney You can use a var vector field and keep updating it. Or, you can choose another mutable collection as needed. Insert is as I've shown using :+ and +:.

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