{
    "book": [
        {
            "category": "reference",
            "author": "Nigel Rees",
            "title": "Sayings of the Century",
            "price": 8.95
        },
        {
            "category": "fiction",
            "author": "Evelyn Waugh",
            "title": "Sword of Honour",
            "price": 12.99
        },
        {
            "category": "fiction",
            "author": "Herman Melville",
            "title": "Moby Dick",
            "isbn": "0-553-21311-3",
            "price": 8.99
        },
        {
            "category": "fiction",
            "author": "J. R. R. Tolkien",
            "title": "The Lord of the Rings",
            "isbn": "0-395-19395-8",
            "price": 22.99
        }
    ]
}

var jsonData = pm.response.json();
// Get list books from response
var books = jsonData.json.book;

// Only for debug
console.log(books);

// Get list of authors, then save to environment
var authors = _.map(books, 'author');

// Need convert to String before save to environment
pm.environment.set("authors", JSON.stringify(authors));

// Only for debug
for (i = 0; i < authors.length; i++){
    console.log(authors[i]);
}

let authors = JSON.parse(pm.environment.get('authors'));

let index = _.random(authors.length - 1);

pm.variables.set("author", authors[index]);