Adding empty list to list of lists

Question

I have list of lists like this:

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

I want to get

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

or

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

Standart concatenation didn't work, so what should I do?

Hi if the answer below worked could you accept it. Solved questions help SO users focus on older unsolved questions. — Harshal Pandya
– Harshal Pandya, Commented May 14, 2013 at 6:32

Usman · Accepted Answer · 2016-07-15 22:01:05Z

1

val l = List(List(1, 2, 3), List(1, 2), List(1))
l: List[List[Int]] = List(List(1, 2, 3), List(1, 2), List(1))

List()+:l
res0: List[List[Int]] = List(List(), List(1, 2, 3), List(1, 2), List(1))

answered Jul 15, 2016 at 22:01

Usman

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Harshal Pandya · Accepted Answer · 2013-05-03 21:59:49Z

0

This works for me.

scala> val ls = List(List(1, 2, 3), List(1, 2), List(1))
ls: List[List[Int]] = List(List(1, 2, 3), List(1, 2), List(1))
scala> val newLs = List()::ls
newLs: List[List[Int]] = List(List(), List(1, 2, 3), List(1, 2), List(1))

answered May 3, 2013 at 21:59

Harshal Pandya

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1 Comment

Luigi Plinge Over a year ago

@qwwdfsad the append operator is :+

dan gleebits · Accepted Answer · 2014-05-01 17:40:09Z

0

ls::List()

is wrong syntax

List()::ls

works but you have to assign it to a new List. You can't modify the original ls because it is immutable.

answered May 1, 2014 at 17:40

dan gleebits

1

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