Map from a list to another type - Is there a better way to do this?

Question

let claimsList  =  
          [ {|cType = "uid"; cValue="1"|};
            {|cType = "name"; cValue="N1"|}; 
            {|cType = "sid"; cValue="sid1"|}; 
            {|cType = "email"; cValue="[email protected]"|}; 
            {|cType = "company"; cValue="Company1"|}]

let email = claimsList
          |> List.tryFind(fun c -> c.cType = "email")
          |> Option.map(fun c -> c.cValue)
let company = claimsList
            |> List.tryFind(fun c -> c.cType = "company")
            |> Option.map(fun c -> c.cValue)
let userId = claimsList
           |> List.tryFind(fun c -> c.cType = "userId")
           |> Option.map(fun c -> c.cValue)

(email, userId, company)

I don't like the fact that I am iterating the list multiple times and looks complicated. Is there a way to simplify this?

Answer 1

If you need to look up claims multiple times, and provided they all have different cTypes, you could convert the list to a map and then lookup in it:

let map = claimsList |> List.map (fun r -> r.cType, r.cValue) |> Map.ofList

let email = map.["email"]
let company = map.["company"]
let userId = map.["uid"]

Note that indexing like map.["email"] will crash at runtime if the key is not present in the map. This is fine if missing keys "shouldn't normally happen", but if you want to handle this case gracefully, use Map.tryFind instead, which will return you an option:

let email = map |> Map.tryFind "email"