Is there a functional programming way to retrieve the first element of a collection?

Question

The list can be empty. I would like to do :

def value = "";
def list = getList()
if (!list.isEmpty()){
   value = list.first().foo 
}

for instance I have found this way :

assert ( [].find()?.foo?:"empty" ) == "empty"
assert ([[foo:"notEmpty1"], [foo:"notEmpty2"]].find()?.foo?:"empty") == "notEmpty1"

Is there a better way ?

Thanks! :)

EDIT:

I got great answer by using [0]

assert ( [][0]?.foo?:"empty" ) == "empty"
assert ([[foo:"notEmpty1"], [foo:"notEmpty2"]][0]?.foo?:"empty") == "notEmpty1"

list is not null but can be empty. So `list?.get(0)` will throws an IndexOutOfBoundsException — Nicolas Labrot, Mar 08 '13 at 15:43
If it is not a `List` but a `Collection` read this post http://stackoverflow.com/questions/1671378/java-get-first-item-from-a-collection — iberbeu, Mar 08 '13 at 15:44
I agree I can use external lib like guava, but i'm looking for a 100% groovy solution. — Nicolas Labrot, Mar 08 '13 at 15:50
In the same post you have it. As groovy can use the libraries of java a java solution is a groovy solution. 100% — iberbeu, Mar 08 '13 at 15:52

score 0 · Answer 1 · edited May 23 '17 at 11:49

0

If it is a List just try

if (!list?.isEmpty()){
    list.get(0);
}

If the list element cannot be null you don't need the ?

If it is a Collection there are several forms to retrieve it. Take a look at this post

edited May 23 '17 at 11:49

Community

answered Mar 08 '13 at 15:45

iberbeu

score 0 · Answer 2 · answered Mar 09 '13 at 07:48

0

I got an answer from tweeter. The statements :

def value = "";
def list = getList()
if (!list.isEmpty()){
   value = list.first().foo 
}

Can be write :

def value = list[0]?.foo?:""

find may be use if the list can contain null values

answered Mar 09 '13 at 07:48

Nicolas Labrot

2 Answers2