前卫管道运营商的怀疑 [英] Foward pipe operator doubt

问题描述

 abs(float x.[1]-float x.[4]))
|> (有趣的x-> x.[0])
 
为什么我不能使用下面的代码? 
 
  (有趣x-> x.[0])(    List.map splitCommas stockData)  
 

解决方案

您必须在List.map周围添加方括号，并告诉编译器第一个x参数是哪种类型(要么显式[类型注释]或隐式地[让推论与Array模块上的函数一起工作来推断]).

您需要它，因为此时编译器没有x的信息，并且不知道它可以expr.[idx]运算符

(fun(x:_ [])-> x.[0])(List.maxBy(fun x-> abs(float x.[1]-float x .[4]))(List.map splitCommas stockData))

//或者
(fun x-> Array.get x 0)(List.maxBy(fun x-> abs(float x.[1]-float x.[4]))(List.map splitCommas stockData))

(对我来说)真正的问题是为什么您要这样做?

from the lesson:
let stockData =
    [ 
      "2012-03-30,32.40,32.41,32.04,32.26,31749400,32.26";
      "2012-03-29,32.06,32.19,31.81,32.12,37038500,32.12";
............................................
      "2012-03-01,31.93,32.39,31.85,32.29,77344100,32.29";
      "2012-02-29,31.89,32.00,31.61,31.74,59323600,31.74"; ]

let splitCommas (x:string) =
    x.Split([|','|])

stockData
|> List.map splitCommas
|> List.maxBy (fun x -> abs(float x.[1] - float x.[4]))
|> (fun x -> x.[0])
Why I can not use the code below instead? and How can i code without pipe?
(fun x -> x.[0])(List.maxBy (fun x -> abs(float x.[1] - float x.[4]))
	List.map splitCommas stockData)

解决方案

you have to add brackets around the List.map and also tell compiler which type is the first x argument (either explicitely [using a type annotation] or implicitely [letting inference operate with a function on Array module to deduce]).

You need it because at this point the compiler has no info on x and doesn't know it can expr.[idx] operator on it

(fun (x: _[]) -> x.[0]) (List.maxBy (fun x -> abs (float x.[1] - float x.[4])) (List.map splitCommas stockData))

// alternatively
(fun x -> Array.get x 0) (List.maxBy (fun x -> abs (float x.[1] - float x.[4])) (List.map splitCommas stockData))

The real question (for me) is why you would want to do that ?

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