如何从记录转换为元组？

Posted 2023-03-17

【中文标题】如何从记录转换为元组？

【英文标题】：How to convert from record to tuple?

【发布时间】：2018-11-09 21:59:40

【问题描述】：

我经常使用 CSV 类型提供程序，它为所有基础数​​据使用元组。我的问题是我遇到了包含大量列的 csv 文件，并发现围绕操作该大小的数据构建基础设施相当麻烦。如何构建一个只更新特定列子集的函数，而无需创建巨大的模式匹配语句？请参阅下面的代码示例。

// I want to generate lots of sample data for the first three columns
// And I would like to avoid creating giant record types in order to
// do this task as the csv's are always changing and the records would
// have to change as well
type CumbersomeCSVRow = // 17 fields now, but imagine 212
    string * string * string * Option<int> * string * 
    Option<int> * string * string * string * string * 
    string * string * Option<float> * string * 
    Option<float> * Option<float> * string

// Here is a sample row of data
let sampleCumbersomeRow : CumbersomeCSVRow = 
    ("First","Second","Third",Some(52),"MSCI",None,"B74A123","",
     "Airlines","Transportation","","",Some(1.04293),"Updated",
     Some(0.95),Some(56.7423),"Measured")

// Record type of the sample data that I want to 'insert' into the cumbersome data type
type FirstThreeStrings = 
     First : string; Second : string; Third : string

// and some instances of the new data
let generatedFrontMatters = 
    // imagine lots of sample data and workflows to create it, hence the records
    seq  for letter in ["A";"B";"C"] -> 
             First  = letter;
              Second = letter + letter
              Third  = letter + letter + letter  

【参考方案1】：

看看FSharp.Reflection 模块

// Your Code --------------------------------------------------

// I want to generate lots of sample data for the first three columns
// And I would like to avoid creating giant record types in order to
// do this task as the csv's are always changing and the records would
// have to change as well
type CumbersomeCSVRow = // 17 fields now, but imagine 212
    string * string * string * Option<int> * string * 
    Option<int> * string * string * string * string * 
    string * string * Option<float> * string * 
    Option<float> * Option<float> * string

// Here is a sample row of data
let sampleCumbersomeRow : CumbersomeCSVRow = 
    ("First","Second","Third",Some(52),"MSCI",None,"B74A123","",
     "Airlines","Transportation","","",Some(1.04293),"Updated",
     Some(0.95),Some(56.7423),"Measured")

// Record type of the sample data that I want to 'insert' into the cumbersome data type
type FirstThreeStrings = 
     First : string; Second : string; Third : string

// and some instances of the new data
let generatedFrontMatters = 
    // imagine lots of sample data and workflows to create it, hence the records
    seq  for letter in ["A";"B";"C"] -> 
             First  = letter;
              Second = letter + letter
              Third  = letter + letter + letter  

// Response ---------------------------------------------------

open FSharp.Reflection

// create a static back matter to append to
// the slicing here is the part that will need to change as the data changes
//      ++ maybe there's a better way to handle this part??
let staticBackMatter = 
    sampleCumbersomeRow
    |> FSharpValue.GetTupleFields
    |> (fun x -> x.[3 .. 16])

// cast the front matter using FSharp.Reflection
let castedFrontMatters = Seq.map FSharpValue.GetRecordFields generatedFrontMatters

// append the data arrays together, create a tuple using reflection, and downcast the result
// to your type
let generatedRows = 
    castedFrontMatters
    |> Seq.map (fun frontArray -> Array.append frontArray staticBackMatter)
    |> Seq.map (fun data -> FSharpValue.MakeTuple(data,typeof<CumbersomeCSVRow>) :?> CumbersomeCSVRow)
    |> Seq.toList

这是否是正确的 F#，我不知道。