Question

请考虑此数据集：

type Deck = JsonProvider<"...">
let dt = Deck.GetSamples()

dt

[{"collectible":true,"health":4,"artist":"Zoltan Boros","type":"MINION","cost":1,"attack":2},
{"collectible":true,"health":8,"artist":"James Ryman","type":"MINION","cost":8,"attack":8},
{"collectible":true,"health":3,"artist":"Warren Mahy", "type":"LAND","cost":2,"attack":2}]

我正在尝试构建一个能够从中提取某些信息的函数，并最终将它们存储在一个较小的数据集中。在给定类似列表的数据集deck的情况下，它应该只考虑key s等于给定value s的卡片。

let rec filter deck key value =
    let rec aux l1 l2 l3 =
        match l1 with
        [] -> []
        | x::xs when x.l2 = l3 -> x::(aux xs key value)
    aux deck key value

例如，

filter dt type minion

应将甲板分成较小的甲板，只有第一张和第二张卡。我认为我在获得这个概念方面做了很少的步骤，但它仍然没有用，抛出了一种错误

FS0072: Lookup on object of indeterminate type based on information prior to
this program point. A type annotation may be needed prior to this program point to 
constrain the type of the object. This may allow the lookup to be resolved.

我应该如何定义key的类型？我尝试使用key : string和key : string list，但没有成功。

Answer 1

您是否尝试重新实施filter？

#if INTERACTIVE
#r @"..\packages\FSharp.Data\lib\net40\FSharp.Data.dll"
#endif

open FSharp.Data

[<Literal>]
let jsonFile = @"C:\tmp\test.json"

type Json = JsonProvider<jsonFile>
let deck = Json.Load(jsonFile)

deck |> Seq.filter (fun c -> c.Type = "MINION")

给我：

val it：seq.Root＆gt; = seq
      [{“collectible”：true，“health”：4，“artist”：“Zoltan Boros”，“type”：“MINION”，“cost”：1，“attack”：2};
       {“collectible”：true，“health”：8，“artist”：“James Ryman”，“type”：“MINION”，“cost”：8，“attack”：8}]

Answer 2

您实际上需要注释l1的类型。

设置l1: something list应该是您想要的。

Key并不提供帮助，因为类型推断是从上到下，x.l2是在aux被调用key作为参数之前

子集JSON数据

2 个答案: