def map = [
1: [lang:"Groovy", isbn: 654, book: "Groovy Pro"],
2: [lang:"Java", isbn: 981, book: "Java Pro"],
3: [lang:"C++", isbn: 236, book: "C++ Pro"],
4: [lang:"Python", isbn: 708, book: "Python Pro"]]
def langs = map.collect{entry -> entry.value.lang}
println langs
println langs.get(0)
/*
run:
[Groovy, Java, C++, Python]
Groovy
*/