CODEWITHSUNDEEP
f#
Khaine775
Khaine775

Reputation: 2765

F# Finding distinct elements in list of tuples

I have a list of tuples:

(string * (int * int)) list
let st = [("a1",(100,10)); ("a2",(50,20)); ("a3",(25,40))]

Where I want to make a function which returns a bool on a few conditions: Both the ints have to be more than 0 and the strings in the list have to be distinct.

So far I have:

let rec inv st = List.forall (fun (a,(n,p)) -> n>0 && p>0) st

But I'm having trouble figuring out how to find out if all the strings in the list are distinct. Any hints?

Upvotes: 1

Views: 321

Answers (2)

Gus
Gus

Reputation: 26174

Use distinctBy:

let inv st =        
    List.length (List.distinctBy fst st) = List.length st && List.forall (fun (a,(n,p)) -> n>0 && p>0) st

or you can combine both checks in a single pipeline:

let inv st =        
    st
    |> List.filter (fun (_,(n,p)) -> n>0 && p>0)
    |> List.distinctBy fst
    |> List.length
    |> (=) (List.length st)

Upvotes: 6

Fyodor Soikin
Fyodor Soikin

Reputation: 80744

The shortest way would be to just compile the list of all distinct strings (via List.distinct) and see if it ended up the same size as the original list:

let allDistinctStirngs = st |> List.map fst |> List.distinct
let allStringsAreDistinct = List.length st = List.length allDistinctStrings

Upvotes: 1

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