How to get a list with odd numbers first, then even numbers attached at end. OCaml-CodePudding

I have to transform a list into a list, where the odds come first and evens after. I have the logic around it but am unsure how to write the code correctly.

The list should be split into 2 lists, one of all odds and one of all evens. Then join the evens to the odds with odds @ evens and output the final list. My code currently is :

let oddfirst = isOdd @ isEven;; 
    let isOdd list= List.allOdd (fun x -> x mod 2!= 0) list;;
    let isEven list= List.allEven (fun y -> y mod 2= 0) list;;

CodePudding user response：

OCaml files are read top to bottom. You are concatenating two elements that are not defined. isOdd and isEven are not lists, they're functions that take int list and return I don't know what since you're using functions that don't exist in the List module.

Your code should look like:

let oddfirst l = 
  let isOdd = List.<find_the_function> (fun x -> x mod 2 <> 0) l in 
  let isEven = List.<find_the_function> (fun x -> x mod 2 = 0) l in 
  isOdd @ isEven

CodePudding user response：

The simplest way is to use the List.partition function:

let oddFirst l =
  let (even, odd ) = List.partition (fun x -> x mod 2 = 0) l in
  odd @ even;;

oddFirst list

CodePudding user response：

Ok so i found out List.filter works best for me. Here is the solution:

let oddfirst l = 
  let isOdd = List.filter (fun x -> x mod 2 != 0) l in 
  let isEven = List.filter (fun x -> x mod 2 = 0) l in 
  isOdd @ isEven