Remove item from groovy list - collections

Question

I am trying to remove an item from groovy list. I've tried following:
List<User> availableUsers = []
availableUsers = workers
for (int i = 0; i < availableUsers.size(); i++) {
if (availableUsers[i].equals(user)){
availableUsers.drop(i)
break
}
}
I've also tried:
availableUsers.remove(user)
In both cases the list gets emptied. Does anyone have any idea what's going on?

Answer 1

Have you tried
availableUsers - user
?
Docu: http://groovy.codehaus.org/groovy-jdk/java/util/List.html#minus(java.lang.Object)
Haven't got much experience with groovy myself, but that's what I would try.

Answer 2

As mentioned above, the answer depends on whether you wish to remove all occurrences of an item...
myList = ['a','b','c', 'c']
myList -= 'c'
assert myList == ['a','b']
...or just the first instance.
myList = ['a','b','c', 'c']
myList.remove(myList.indexOf('c'))
assert myList == ['a','b','c']
I'm still new to Groovy myself, but one of the underlying principles is that it almost always has a way of making common tasks trivial one-liners. Adding or removing items from a collection would certainly qualify.

Answer 3

Fildor is right, but if you only want ot remove the first occurence of user in your list (minus will remove all occurrences), you will probably need something like:
list = list.indexOf( user ).with { idx ->
if( idx > -1 ) {
new ArrayList( list ).with { a ->
a.remove( idx )
a
}
}
else list
}

Answer 4

I had a related requirement but wanted to remove more than one items knowing their index position. It was not easy to do in a loop as after removing the first item, the index position of the remaining ones changes. It seemed easy to first create a list with items to be removed and then use the collections minus operation to remove them from the target list. Here is an example:
myList=['a','b','c','d']
remove=[0,1,2] //index list of list elements to remove
removeList=myList[remove]
println removeList
assert ['d']== myList.minus(removeList)
LIMITATION:if the value at index is present multiple times in target list, ALL instances are removed.
So, if
myList=['a','b','c','d','a','e']
remove=[0,1,2]
removeList=myList[remove]
assert myList.minus(removeList)== ['d','e']
the result will be d,e