Clojure List -> Vector

Question

I need to create a function. Within this I need the following to happen:

List 1: '(a 5 6)
List 2: '(c 8 10)
List 3: '(d 4 9)

Above are the lists. I need to ignore the 1st column of each list (this being a, c and d.) and then put the 2nd column in a vector. Then do the same for the 3rd column but a separate vector. Once this is done I'll carry out some small arithmetic between the two and write the results of each into a third vector.

I have very little Clojure experience and come from a Java background. I've tried to use let

By doing so I've only been able to create a var which stores the 2nd and 3rd item in a single list only. (e.g. List 1's 5 & 6.) However I need the vector to be [5 8 4].

This sounds like matrix arithmetic. Depending on what else you want to do with the data, core.matrix might be useful. — Mars
– Mars, Commented Oct 27, 2015 at 4:06

Leon Grapenthin · Accepted Answer · 2015-10-25 15:30:28Z

4

(defn answer [& [list-1 list-2 list-3 :as lists]]
   (->> lists                    ; ((a 5 6) (c 8 10) (d 4 9))
        (map rest)               ; ((5 6) (8 10) (4 9))
        (apply map vector)       ; ([5 8 4] [6 10 9])
        (apply small-arithmetic) ; (small-arithmetic [5 8 4] [6 10 9])
  ))

assuming small-arithmetic is a function taking the desired two vectors and returning the third vector.

edited Oct 25, 2015 at 15:30

answered Oct 25, 2015 at 15:15

Leon Grapenthin

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9 Comments

DoogJames Over a year ago

Can you just run me through your answer please? So lists 1, 2 and 3 are all within a list. So a list of lists. Would they be put in the function as a parameter like that? If it's a list of lists would this change your answer at all..

Leon Grapenthin Over a year ago

I have declared a variadic function to collect the three argument lists in lists. (answer list-1 list-2 list-3) is the intended invocation. An equivalent declaration would be (defn answer [list-1 list-2 list-3] (->> [list-1 list-2 list-3] ...;(as above)

Leon Grapenthin Over a year ago

If the input is a list of lists you chould just (defn answer [lists] ...) and invoke it e. g. (answer [list-1 list-2 list-3])

DoogJames Over a year ago

I'll give it a run through, I'm fairly confident I'm going to struggle with its implementation though so I'll keep it open for a while!

DoogJames Over a year ago

How would I do the function for the small-arithmetic?

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