How to remove empty lists from list using scala?

Question

I have following list structure -

List(List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List({"esx":"192.168.20.52","vm":" naa.60a9800042704577762b45634476337a ","datastore":"","vNic":"","portGroupVLan":"","vSwitch":"","physicalNic":"","lunName":"lun_30102014_101347)","writeIops":44998,"readIops":1635,"latency":47008,"serialNumber":"BpEwv+EcDv3z","usedSize":0,"totalSize":4,"availableSize":4,"throughput":null}, (), ()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List((), (), ()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List((), (), ()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List(()), List((), (), ()))

I want to remove all empty lists from above . I want output as -

List({"esx":"192.168.20.52","vm":" naa.60a9800042704577762b45634476337a ","datastore":"","vNic":"","portGroupVLan":"","vSwitch":"","physicalNic":"","lunName":"lun_30102014_101347)","writeIops":44998,"readIops":1635,"latency":47008,"serialNumber":"BpEwv+EcDv3z","usedSize":0,"totalSize":4,"availableSize":4,"throughput":null})

How do I get above output by using scala??

Flatten it! That will remove the empty lists whilst collapsing the structure by one dimension. — Boris the Spider
– Boris the Spider, Commented Nov 6, 2014 at 11:42

Diego Martinoia · Accepted Answer · 2014-11-06 12:11:17Z

2

If your input is like that, i.e. you only have list(list(list())) depth, a double call to flatten will solve it.

val x = yourList
x.flatten.flatten

if your list has empty lists at various depths, you need to constantly flatten until you reach a fixed point:

val x = yourList
var y = x.flatten
var z = y.flatten
while (y != z) {
   y = z
   z = z.flatten
y

Hope that helps :)

edited Nov 6, 2014 at 12:11

answered Nov 6, 2014 at 11:56

Diego Martinoia

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4 Comments

user3322141 Over a year ago

But I want only non empty list only... Can you see my expected output and input given please

Diego Martinoia Over a year ago

Flattening removes empty lists: List(List(), List(1)).flatten == List(1) I assume that your actual code is not List(()) but List(List()), otherwise you don't have empty lists, you have lists filled with a single instance of the Unit type (VERY different thing).

kiritsuku Over a year ago

your while loop will never typecheck.

Diego Martinoia Over a year ago

You are right. My bad. Can you edit my response / add a response that does the same thing but with type check passing?

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