将元组序列写入CSV文件F# [英] Write a sequence of tuples to a csv file f#

问题描述

我试图将一组元组写入一个csv，但是普通的File.WriteAllLines被一组元组所重载.

Iam trying to write a sequence of tuples to a csv, but the normal File.WriteAllLines is overloaded by a sequence of tuples.

因此，我试图将元组展平为一系列字符串.

I have tried therefore to flatten my tuples into a sequence of strings.

这是我的代码:-

open System;;
open Microsoft.FSharp.Reflection;;

let tupleToString (t: string * float) = 
        if FSharpType.IsTuple(t.GetType()) 
        then String.Format("{0},{1}", fst t, snd t)
        else "";;

    let testTuple = ("monkey", 15.168);;

    tupleToString(testTuple);;

let testSeqTuple = [("monkey", 15.168); ("donkey", 12.980)];;

let allIsStrings (t:seq<string * float>) = Seq.collect tupleToString t;;

allIsStrings(testSeqTuple);;

当我仅在一个元组上使用"tupleToString"时，结果就很好.

When I use "tupleToString" on just one tuple the results are just fine.

但是allIsStrings的Seq.collect部分返回按字符分解的元组.

However the Seq.collect part of allIsStrings returns the tuples broken down by characters.

我也尝试过Seq.choose和Seq.fold，但是它们只会引发错误.

I have also tried Seq.choose and Seq.fold, but these simply throw errors.

任何人都可以建议我应该使用序列模块中的什么功能-或建议可以在元组上工作的File.WriteAllLines的替代方案吗?

Can anyone advise as to what function from the sequence module I should be using - or advise on an alternative to File.WriteAllLines that would work on a tuple?

推荐答案

您需要使用Seq.map将列表的所有元素转换为string，然后使用Array.ofSeq来获取可以传递给WriteAllLines:

You need to use Seq.map to convert all elements of a list to string and then Array.ofSeq to get an array which you can pass to WriteAllLines:

let allIsStrings (t:seq<string * float>) = 
  t |> Seq.map tupleToString
    |> Array.ofSeq

此外，在您的tupleToString函数中，您无需使用反射来检查参数是否为元组.它始终是一个元组，因为这由类型系统保证.所以你可以这样写:

Also, in your tupleToString function, you do not need to use reflection to check that the argument is a tuple. It will always be a tuple, because this is guaranteed by the type system. So you can just write:

let tupleToString (t: string * float) = 
  String.Format("{0},{1}", fst t, snd t)      

如果您想对具有任意数量参数的元组使用此功能，您可以 使用反射(但这是更高级的主题).以下获取元组的元素，将它们全部转换为字符串，然后使用逗号将它们连接起来:

You could use reflection if you wanted to make this work for tuples with arbitrary number of parameters (but that is a more advanced topic). The following gets elements of the tuple, converts them all to string and then concatenates them using a comma:

let tupleToString t = 
  if FSharpType.IsTuple(t.GetType()) then
    FSharpValue.GetTupleFields(t)
    |> Array.map string
    |> String.concat ", "
  else failwith "not a tuple!"

// This works with tuples that have any number of elements
tupleToString (1,2,"hi")
tupleToString (1.14,2.24)

// But you can also call it with non-tuple and it fails
tupleToString (new System.Random())

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