Removing an element from MutableList in Scala

Question

I have a MutableList and I want to remove an element from it but I cannot find the appropriate method. There is a method to remove element from ListBuffer like this:

val x = ListBuffer(1, 2, 3, 4, 5, 6, 7, 8, 9)
x -= 5

I am unable to find an equivalent method on MutableList.

possible duplicate of [Removing elements from mutable lists](http://stackoverflow.com/questions/11575050/removing-elements-from-mutable-lists) — Ryan Leach, Jul 06 '15 at 11:09
the question you refferd was has the answers for ArrayBuffer i have searched and found the same solution for ListBuffer but that solution doesnot work with MutableList that i am using — M.Ahsen Taqi, Jul 06 '15 at 12:28
I wouldn't recommend you to use them - they're pretty tricky: https://github.com/scala/scala/commit/3cc99d7b4aa43b1b06cc837a55665896993235fc — dk14, Jul 06 '15 at 14:45

score 9 · Accepted Answer · edited May 23 '17 at 11:44

MutableList lacks -= and --= because it does not extend the Shrinkable trait. Various motivations for this can be found here.

MutableList does have diff, filter, and other methods which can help you in case you are in a situation where reassigning a variable (or instantiating a new variable) might be an option, and performance concerns aren't paramount:

var mylist = MutableList(1, 2, 3)
mylist = mylist diff Seq(1)
val myNewList = mylist.filter(_ != 2)
val indexFiltered = mylist.zipWithIndex.collect { case (el, ind) if ind != 1 => el }

You can often use ListBuffer instead of MutableList, which will unlock the desired -= and --= methods:

val mylist = ListBuffer(1, 2, 3)
mylist -= 1 //mylist is now ListBuffer(2, 3)
mylist --= Seq(2, 3) //mylist is now empty

score 1 · Answer 2 · answered Jul 06 '15 at 14:53

It's not the answer, just to warn you about problems (at least in 2.11.x):

//street magic
scala> val a = mutable.MutableList(1,2,3)
a: scala.collection.mutable.MutableList[Int] = MutableList(1, 2, 3)
scala> a += 4
res7: a.type = MutableList(1, 2, 3, 4)
scala> a
res8: scala.collection.mutable.MutableList[Int] = MutableList(1, 2, 3, 4)
scala> a ++= List(8,9,10)
res9: a.type = MutableList(1, 2, 3, 4, 8, 9, 10)
scala> val b = a.tail
b: scala.collection.mutable.MutableList[Int] = MutableList(2, 3, 4, 8, 9, 10)
scala> b.length
res10: Int = 6
scala> a.length
res11: Int = 7
scala> a ++= List(8,9,10)
res12: a.type = MutableList(1, 2, 3, 4, 8, 9, 10, 8, 9, 10)
scala> b += 7
res13: b.type = MutableList(2, 3, 4, 8, 9, 10, 7)
scala> a
res14: scala.collection.mutable.MutableList[Int] = MutableList(1, 2, 3, 4, 8, 9, 10, 7) 
scala> b
res15: scala.collection.mutable.MutableList[Int] = MutableList(2, 3, 4, 8, 9, 10, 7)
scala> a ++= List(8,9,10)
res16: a.type = MutableList(1, 2, 3, 4, 8, 9, 10, 7)

This example is taken from some gist - I've posted it on facebook with #devid_blein #street_magic tags, but can't find original link on the internet.

Removing an element from MutableList in Scala

2 Answers2