Add an entry to every element in a nested data structure

Question

I currently use a data structure like this:

(def sample-board 
 [[{:mine true} {:warn 2 } {:warn 1} { }]
 [{:warn 2 } {:mine true} {:warn 1} { }]
 [{:warn 1 } {:warn 1 } {:warn 2} {:warn 1 }]
 [{ } { } {:warn 1} {:mine true}]])

Now I want to create a copy of the first structure and each element should be supplemented with :explored true.

My approach so far looks like this:

(def sample-board-solved
 (map (partial map 
 (partial conj {:explored true})) 
 sample-board))

I don't find the approach very appealing though. I thought about using for instead or maybe recur in combination with update-in but I did not bring it to work yet.

I'd be glad on suggestions how to improve the code.

Answer 1

You could maybe make your solution a bit neater by using a lambda in place of one of your partials. assoc might be a little clearer in purpose than a conj as well:

(def sample-board-solved
 (map (partial map #(assoc % :explored true))
 sample-board))

Using map like this will return things in sequences rather than vectors like the input data. If it's particularly important that you get vectors out you can always use mapv

• BenC: +1. Also, if this pattern happens a lot, OP could define a 2-depth or "board-cell-level" map: (defn mapmap [f coll] (map (partial map f) coll))