在F#中有一种惯用的方法是在列表/ seq /数组中向前看并使用在处理当前项目时学到的信息吗?在我的场景中,还需要改变(或以其他方式存储它已更改的事实)前面的项目,以便依次正确处理它。我正在实施一些相当愚蠢的业务规则,这样的模式或技术会很有用。
现在我正在使用累加器来存储信息,然后在处理每个数据时改变数组的项目。如下面的简化示例所示,这感觉有点笨拙。我正在解决的问题的实际业务规则更复杂,所以如果有更好的方法,我宁可不跋涉这条路。基本上,我希望摆脱graceMonths
类型中的Acc
,而是通过向前看列表/ seq /数组来解决这些月份。
模拟示例:当工人每个月达到所需的生产水平时,他们会获得某种类型的奖励。如果他们未能达到理想水平,他们可以通过超过接下来几个月的水平来弥补它。同样,他们可以将过剩的生产储存在未来的月份,以供不足之处使用。以下脚本显示了一个示例。
type CalendarMonth =
{ year : int
month : int }
type InMonth =
{ month : CalendarMonth
prodCount : int }
type OutMonth =
{ month : CalendarMonth
prodCount : int
borrowedFrom : InMonth list
metProd : bool }
type OutMonthAcc =
{ outMonth : OutMonth
notUsed : InMonth list }
type IndexOutMonth =
{ index : int
outMonth : OutMonth }
type Acc =
{ index : int
graceMonths : IndexOutMonth list
bankedProd : InMonth list
arrRef : OutMonth array }
type GraceAcc =
{ processed : IndexOutMonth list
notUsed : InMonth list }
let createMonth y m c =
{ InMonth.month =
{ year = y
month = m }
prodCount = c }
let toOutPutMonth (x : InMonth) =
{ month = x.month
prodCount = x.prodCount
borrowedFrom = []
metProd = false }
let toSimple (x : OutMonth) = sprintf "year: %i, month: %i, metProd: %b" x.month.year x.month.month x.metProd
let solveWithBanked desiredProd bank m =
let useProd (acc : OutMonthAcc) inMonth =
let m = acc.outMonth
if m.metProd then
{ acc with notUsed = inMonth :: acc.notUsed }
else
let borrowed = m.borrowedFrom |> List.sumBy (fun x -> x.prodCount)
let needed = desiredProd - (m.prodCount + borrowed)
match inMonth.prodCount with
| x when x < needed ->
{ outMonth = { m with borrowedFrom = inMonth :: m.borrowedFrom }
notUsed = acc.notUsed }
| x when x > needed ->
let newInMonth = { inMonth with prodCount = inMonth.prodCount - needed }
let newOutMonth =
{ m with borrowedFrom = newInMonth :: m.borrowedFrom
metProd = true }
{ outMonth = newOutMonth
notUsed = newInMonth :: acc.notUsed }
| _ ->
{ outMonth =
{ m with borrowedFrom = inMonth :: m.borrowedFrom
metProd = true }
notUsed = acc.notUsed }
bank |> List.fold useProd { outMonth = m
notUsed = [] }
let solveGrace desiredProd bank (graceLst : IndexOutMonth list) =
let useBank acc iOutMonth =
let result = iOutMonth.outMonth |> solveWithBanked desiredProd acc.notUsed
if result.outMonth.metProd then
let iMonth =
{ index = iOutMonth.index
outMonth = result.outMonth }
{ processed = iMonth :: acc.processed
notUsed = result.notUsed }
else { acc with processed = iOutMonth :: acc.processed }
graceLst
|> List.sortBy (fun x -> x.index)
|> List.fold useBank { processed = []
notUsed = bank }
let solve desiredProd acc m =
match m.prodCount < desiredProd with
| true -> // less
let result = m |> solveWithBanked desiredProd acc.bankedProd
if result.outMonth.metProd then
acc.arrRef.[acc.index] <- result.outMonth
{ acc with index = acc.index + 1
bankedProd = result.notUsed }
else
let iMonth =
{ IndexOutMonth.index = acc.index
outMonth = m }
{ acc with index = acc.index + 1
graceMonths = iMonth :: acc.graceMonths }
| false -> // greater
let newM =
{ index = acc.index
outMonth = { m with metProd = true } }
let newIn =
{ InMonth.month = m.month
prodCount = m.prodCount - desiredProd }
let result = acc.graceMonths |> solveGrace desiredProd (newIn :: acc.bankedProd)
let solved, unsolved = result.processed |> List.partition (fun x -> x.outMonth.metProd)
newM :: solved |> List.iter (fun x -> acc.arrRef.[x.index] <- x.outMonth)
{ acc with index = acc.index + 1
graceMonths = unsolved
bankedProd = result.notUsed }
let jan = createMonth 2013 01 4
let feb = createMonth 2013 02 4
let mar = createMonth 2013 03 6
let apr = createMonth 2013 04 7
let may = createMonth 2013 05 4
let jun = createMonth 2013 06 4
let arr =
jan :: feb :: mar :: apr :: may :: jun :: []
|> Array.ofList
|> Array.map toOutPutMonth
arr |> Array.fold (solve 5) { index = 0
graceMonths = []
bankedProd = []
arrRef = arr }
let result =
arr
|> Array.map toSimple
|> List.ofArray
result
的值应显示除6月以外的所有月份生产。这是F#中的正确方法还是有更好的方法?
答案 0 :(得分:1)
这是我在这里尝试的方法:
对于我来说,前两点似乎是不言自明的,至于第三点,这里是余额函数的草案和示例用法:
let (|Lt|Eq|Gt|) (a, b) =
if a = b
then Eq
elif a > b then Gt else Lt
let rec balance below above balanced =
match below, above with
| (x, required)::xs, (y, available)::ys ->
match required, available with
| Lt -> balance xs ((y, available - required) :: ys) (x::balanced)
| Eq -> balance xs ys (x::y::balanced)
| Gt -> balance ((x, required - available) :: xs) ys (y::balanced)
| _, _ ->
below, above, balanced
balance [("a", 4); ("b", 1)] [ ("c", 2); ("d", 2) ] [ "e" ]
balance [("a", 1); ("b", 1)] [ ("c", 2); ("d", 2) ] [ "e" ]
基本上你是并行地走两个列表,从一个列表中“取”并向另一个列表“添加”,直到你用完两个列表。剩下的是做平衡的最佳尝试。
通常,您希望在编写F#代码时使用像List模块这样的集合API,但是记住当您的用例似乎不适合现有方案时,您总是可以回退到“原始”递归。 / p>