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Map.ofList comparison
f#

[link:msdn.microsoft.com]

How can I do this with an FSharp Map?

let ducks = Collections.Generic.Dictionary<string,int> (StringComparer.OrdinalIgnoreCase)

ducks.["duck"] <- 1

ducks.["Duck"] <- 2

ducks.["Goose"] <- 3

let duckCount = ducks.Count

I can do this:

let ducks =

Map.ofList

[

"duck", 1

"Duck", 2

"Goose", 3

]

but how do I make it so that it is OrdinalIgnoreCase?

.

The F# Map/Set APIs don't support a custom comparer; if you want that functionality, you'd create a wrapper type for the key. E.g. create a "IgnoreCaseString" type that just holds a string and has an IComparable implementation that is case-insensitive, and then have the Map hold objects of that type (rather than strings) as keys.

By on 10/28/2009 3:51 PM ()

Actually, you can use a custom comparer if you use the Powerpack and Caml-compatibility functions. But this is somewhat cumbersome, and you don't have most of Map functions (the library improvements didn't apply to the fspack):

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let M = Map.Make<string,int> (fun x y -> compare (x.ToLower()) (y.ToLower()))


let ducks = List.fold (fun acc (k,v) -> M.add k v acc) M.empty ["duck", 1; "Duck", 2; "Goose", 3]

Brian's suggestion is probably the best choice.

Laurent.

By on 10/29/2009 3:09 AM ()

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