groovy sublist removal - list

Question

I have a list:
def clc = [[1, 15, 30, 42, 48, 100], [58, 99], [16, 61, 85, 96, 98], [2, 63, 84, 90, 91, 97], [16, 61, 85, 96], [23, 54, 65, 95], [16, 29, 83, 94], [0, 31, 42, 93], [33, 40, 51, 56, 61, 62, 64, 89, 92], [0, 63, 84, 90, 91]]
and a sublist
def subclc = [[1, 15, 30, 42, 48, 100], [58, 99], [16, 61, 85, 96, 98], [2, 63, 84, 90, 91, 97]]
I need to remove sublist from original list
I do so:
subclc.each{
clc.remove(it)
}
but it throws an exceprion Exception in thread "main" java.util.ConcurrentModificationException
I do not understand where is problem and how to solve the problem

Answer 1

Short answers:
For more groovyness and immutability, preserving the original list:
def removed = clc - subclc
assert removed == [[16, 61, 85, 96], [23, 54, 65, 95], [16, 29, 83, 94], [0, 31, 42, 93], [33, 40, 51, 56, 61, 62, 64, 89, 92], [0, 63, 84, 90, 91]]
And the java way, changing the original list:
clc.removeAll subclc
assert clc == [[16, 61, 85, 96], [23, 54, 65, 95], [16, 29, 83, 94], [0, 31, 42, 93], [33, 40, 51, 56, 61, 62, 64, 89, 92], [0, 63, 84, 90, 91]]
Long answer:
You are Iterator-ing through a list while changing the list. In this case you are better using Iterator.remove(), which is being abstracted by the foreach loop.
When you change the list using the foreach loop, you bump into the iterator checks for modification using checkForComodification(). Getting the iterator explicitly works:
list1 = [10,20,30,40,50,60,70,80,90]
list2 = [50,60,80]
def iter = list1.iterator()
while (iter.hasNext()) {
def item = iter.next()
if (list2.contains(item)) iter.remove()
}
assert list1 == [10,20,30,40,70,90]
Or you can use indexes. Note you need to control the index:
list1 = [10,20,30,40,50,60,70,80,90]
list2 = [50,60,80]
for (int i = 0; i < list1.size(); i++) {
def item = list1[i]
if (list2.contains(item)) { list1.remove i-- }
}
assert list1 == [10,20,30,40,70,90]