Figuring out the difference between map and apply in Clojure...

apply-vs-map.clj

; Define a vector of vectors
(def input [[1,2,3],[1,3,4],[1,5,6]])

; Calling the 'list' function on this:
user=> (list input)
; Gives us a single item list whose one and only member is this
; vector of vectors:
([[1 2 3] [1 3 4] [1 5 6]])

; Mapping the 'list' function to input _applies_
; 'list' to the set of first items in input, followed by applying it to the set
; of second items in input, followed by applying it to the set of third items:
user=> (map list input)
; This gives us a list whose members are single element lists, where the single
; element is the vector list was mapped to.
(([1 2 3]) ([1 3 4]) ([1 5 6]))

; But if we 'apply' the 'map list' function to the input collection:
user=> (apply map list input)
; Then 'apply' extracts the vectors from the vector of vectors to create
; an argument list which is then passed to 'map list':
((1 1 1) (2 3 5) (3 4 6))

; If we were to do the unpacking by hand we and then pass the individual 
; vectors to map list:
user=> (map list [1,2,3],[1,3,4],[1,5,6])
; we'd get the same result:
((1 1 1) (2 3 5) (3 4 6))