Groovy not in collection

The groovy way to see if something is in a list is to use "in"

   if('b' in ['a','b','c'])

However how do you nicely see if something is not in a collection?

  if(!('g' in ['a','b','c']))

Seems messy and the "!" is hidden to the casual glance. Is there a more idiomatic groovy way to do this?

Thanks!

Another way to write it is with contains, e.g.

if (!['a', 'b', 'c'].contains('b'))

It saves the extra level of parentheses at the cost of replacing the operator with a method call.

I think there is no not in pretty syntax, unfortunately. But you can use a helper variable to make it more readable:

def isMagicChar = ch in ['a', 'b', 'c']
if (!isMagicChar) ...

Or, in this case, you may use a regex :)

if (ch !=~ /[abc]/) ...

You can add new functions:

Object.metaClass.notIn = { Object collection ->
    !(delegate in collection)
}


assert "2".notIn(['1', '2q', '3'])
assert !"2".notIn(['1', '2', '3'])

assert 2.notIn([1, 3])
assert !2.notIn([1, 2, 3])

assert 2.notIn([1: 'a', 3: 'b'])
assert !2.notIn([1: 'a', 2: 'b'])

More readable, I'm not sure:

assert ['a','b','c'].any{it == 'b'}
assert ['a','b','c'].every{it != 'g'}

For your example:

if (['a','b','c'].every{it != 'g'})

---

A few months ago, I suggested a new operator overloading ! (not operator). Now, maybe you can use any odd number of exclamations ;)

if(!!!('g' in ['a','b','c']))

Just for the sake of completeness, and for people reaching this thread post-2020, Groovy 3.0.0 introduced the !in operator.

As per the OP example, it would be used like that:

if ('g' !in ['a','b','c'])

According to Grails documentation about creating criteria here, you can use something like this:

not {'in'("age",[18..65])}

In this example, you have a property named "age" and you want to get rows that are NOT between 18 and 65. Of course, the [18..65] part can be substituted with any list of values or range you need.

Regarding one of the original answers:

if (!['a', 'b', 'c'].contains('b'))

Somebody mentioned that it is easy to miss the ! because it's far from the method call. This can be solved by assigning the boolean result to a variable and just negate the variable.

def present = ['a', 'b', 'c'].contains('b')
if (!present) {
    // do stuff
}

The contains(string) method is nice and simple to read if something is contained or not contained in the list to be checked against. Take a look the example below for more insight.

EXAMPLE

//Any data you are looking to filter  
List someData = ['a', 'f', 'b', 'c', 'o', 'o']

//A filter/conditions to not match or match against
List myFilter = ['a', 'b', 'c'] 

//Some variables for this example
String filtered, unfiltered 

//Loop the data and filter for not contains or contains
someData.each {
   if (!myFilter.contains(it)){
      unfiltered += it
   } else {        
      filtered += it
   }
}

assert unfiltered = "foo"
assert filtered = "abc"

CONTAINS( )

Parameters: text - a String to look for.

Returns: true if this string contains the given text

source

What about disjoint ?

def elements = [1, 2, 3]
def element = 4
assert elements.disjoint([element])
element = 1
assert !elements.disjoint([element])

Bonus : it stops iterating when an element match