Groovy .each vs .collect

Question

As part of beginners Groovy workshop, We've been iterating over the following list (fromJson.secrets):

[[floors:10, street:emaseS, url:http://plywoodpeople.com/wp-content/uploads/2012/03/kermit_the_frog.jpg], [floors:2, street:emaseS, url:http://36.media.tumblr.com/tumblr_lp9bg9Lh2x1r0h9bqo1_500.jpg], [floors:2, street:yawdaorB, url:https://montclairdispatch.com/wp-content/uploads/2013/07/broadway1.jpg], [floors:5, street:emaseS, url:AAA], [floors:2, street:yawdaorB, url:AAA], [floors:6, street:albmaR aL, url:AAA], [floors:1, street:teertS llaW, url:AAA], [floors:6, street:daoR yebbA, url:AAA], [floors:3, street:teertS llaW, url:AAA], [floors:4, street:dlirehstoR, url:AAA]]

The original plan was to use .collect, however it looks like using .each produced the same results (iterated over the list...).

The questions is, can someone help me to understand the difference between the methods in regard to my use case and in general

each:

reversed_streets = fromJson.secrets.each {
    it.street = it.street.reverse()
    it
}

collect:

reversed_streets = fromJson.secrets.collect {
    it.street = it.street.reverse()
    it
}

Answer 1

each returns the input to each. Your code there manipulates it.street in place. So you get back your original list, where each street got reversed. With the collect you create a new list with the manipulated items. So the apparent result is the same, but the difference is that you created a new container, but still your original has been tampered with. A simple rule of thumb: each is used for side effects (which is your example). While collect is used to create something new (e.g. map)