Remove item from groovy list

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?

Solution 1

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
}

Solution 2

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.

Solution 3

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.

Comments

[Phat H. VU]

Minus operator for list is NOT a best choice when you are dealing with large lists and their data is complicated. Refer this : rewoo.wordpress.com/2012/11/19/…

[Fildor]

@PhatH.VU 1. Make it run, 2. make it run correctly, 3. make it run fast. In exactly that order :D But of course, you are right.