从现有价值中投射新价值 [英] Project new values from existing value

问题描述

我正在写我的第一个F#程序，目的只是为了学习F#.

I'm writing my very first F# program, the aim being simply to learn F#.

我想要提供的是日期列表，以及这些日期的属性(例如DayOfWeek，DayOfMonth).我已经设法提供了日期列表，并且我知道.net Framework为我提供了提取所有属性所需的一切，但我不知道如何将属性添加为列表中的新列. 这是我到目前为止的内容:

What I want to is provide a list of dates, and attributes (e.g.DayOfWeek, DayOfMonth) of those dates. I have managed to provide the list of dates and I know that the .net Framework gives me everything I need to extract all the attributes, I just can't figure out how to add the attribute as new columns in my list. Here's what I have so far:

type Span = Span of TimeSpan with
 static member (+) (d:DateTime, Span wrapper) = d + wrapper //this is defining the + operator
 static member Zero = Span(new TimeSpan(0L))

type Dates() = 

 let a = DateTime.Parse("01/12/2013")
 let b  =DateTime.Parse("02/12/2013")
 let ts = TimeSpan.FromDays(1.0)
 member this.Get() = [a .. Span(ts) .. b]

let mydates = new Dates()
mydates.Get()

运行该代码时，我得到一个DateTime值列表，该列表中有2条记录.我现在可以做这样的事情:

When I run that code I get a list of DateTime values, with 2 records in the list. I can now do something like this:

mydates.Get() |> List.map (fun x -> x.DayOfWeek);;

返回:

val it:DayOfWeek list = [Sunday;星期一]

val it : DayOfWeek list = [Sunday; Monday]

或

mydates.Get() |> List.map (fun x -> x.DayOfYear);;

返回:

val it:int list = [335; 336]

val it : int list = [335; 336]

那太好了，但是我想做的是投影一个包含2个列"的列表(如果列是正确的单词)，以便我的输出是(类似):

That's all great, however what I would like to do is project a list that has 2 "columns" (if columns is the right word) so that my output is (something like):

val it:int list = [(Sunday，335); (星期一，336)]

val it : int list = [(Sunday,335); (Monday,336)]

我希望这可以解释我的追求.

I hope that explains what I'm after.

谢谢

杰米

推荐答案

在您的示例中，解决方案很简单，使地图返回像这样的元组

For your example, the solution is simple, make the map return a tuple like so

mydates.Get() |> List.map (fun x -> x.DayOfWeek,x.DayOfYear);;

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