F＃按一个以上值分组并进行汇总

Question

F＃。 我有以下类型的清单transactions ：

type Transaction(Debitor: string, Spend:float, Creditor:string)  = 
     member this.Debitor = Debitor
     member this.Spend = Spend
     member this.Creditor = Creditor

我知道如何按一个值分组。 举例来说，我想按属性Debitor ，可以轻松地将该属性用作该组的Key：

let tsGroupDebitor =
    transactions        
    |> Seq.groupBy(fun ts -> ts.Debitor)

但是，我无法按两个值分组，例如Debitor和Creditor 。 理想情况下，我希望在为Spend属性应用聚合函数“ Sum”的同时考虑Debitor和Creditor 。

换句话说 ，我想实现以下LINQ查询的F＃等效项：

 var transactions_GroupSameDebitorCreditor = 
     transactions
     .GroupBy(ts => new { ts.Debitor, ts.Creditor }) // group by multiple values
     .Select(gr => new 
            {
                Debitor = gr.Key.Debitor,
                Debit = gr.Sum(trans => trans.Spend), //sum the trans values per grouped relationships
                Creditor = gr.Key.Creditor
            });

返回匿名类型的IEnumerable的位置。

Answer 1

您可以使用元组作为组键，如下所示：

let tsGroupDebitor =
    transactions        
    |> Seq.groupBy(fun ts -> (ts.Debitor, ts.Creditor))

如果要汇总每个组的事务以汇总Spend属性，可以执行以下操作：

let tsGroupDebitor =
        transactions        
        |> Seq.groupBy(fun ts -> (ts.Debitor, ts.Creditor))
        |> Seq.map(fun ((debitor, creditor), values) -> ( debitor, creditor, values |> Seq.sumBy (fun t -> t.Spend)))

请注意，我如何将模式匹配与模式((debitor, creditor), values) ，以便能够访问组密钥的两个部分以及每个组（ values ）的交易顺序

Answer 2

let sumTransactions (transactions: Transaction list) =
    transactions
    |> Seq.groupBy(fun ts -> (ts.Creditor, ts.Debitor))
    |> Seq.map (fun ((cred, deb), ts) -> 
                    let s = ts |> Seq.sumBy (fun t -> t.Spend)
                    Transaction(deb, s , cred))