Clojure apply vs map

Question

I have a sequence (foundApps) returned from a function and I want to map a function to all it\'s elements. For some reason, apply and count work for th

Answer 1

A little explanation might help. In general you use apply to splat a sequence of elements into a set of arguments to a function. So applying a function to some arguments just means passing them in as arguments to the function, in a single function call.

The map function will do what you want, create a new seq by plugging each element of the input into a function and then storing the output. It does it lazily though, so the values will only be computed when you actually iterate over the list. To force this you can use the (doall my-seq) function, but most of the time you won't need to do that.

If you need to perform an operation immediately because it has side effects, like printing or saving to a database or something, then you typically use doseq.

So to append "foo" to all of your apps (assuming they are strings):

(map (fn [app] (str app "foo")) found-apps)

or using the shorhand for an anonymous function:

(map #(str % "foo") found-apps)

Doing the same but printing immediately can be done with either of these:

(doall (map #(println %) found-apps))

(doseq [app found-apps] (println app))