题
是否有更好的代码,不需要将序列转换为列表?
let rec addentry map keys =
match keys with
| ((i,j) :: tail) -> Map.add (i,j) ((inputd.[i]).[j]) (addentry map tail)
| ([]) -> map
addentry Map.empty (Cartesian keys1 keys2 |> Seq.toList)
. 解决方案
This is a great place to use Seq.fold
. It collapses a collection down into a single value.
Cartesian keys1 keys2
|> Seq.fold (fun map (i, j) ->
let value = (inputd.[i]).[j]
Map.add (i, j) value map) Map.empty
其他提示
Cartesian keys1 keys2
|> Seq.map (fun (i, j) -> ((i, j), (inputd.[i]).[j]))
|> Map.ofSeq
As a complement to the previous answers, if you want to be able to pattern-match sequences, you can define an active pattern:
let (|Cons|Nil|) s =
if Seq.isEmpty s then
Nil
else
Cons(Seq.head s, Seq.skip 1 s)
let rec addentry map keys =
match keys with
| Cons((i,j), tail) -> Map.add (i,j) ((inputd.[i]).[j]) (addentry map tail)
| Nil -> map
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