将float [，]转换为f#中的列表? [英] Converting float[,] to list in f#?

问题描述

我有一个可以很好地用于列表的功能，但是该功能的输入来自外部系统/语言，是float[,].

I have a function that works fine for lists however the input to the function comes as float[,] from external system / language.

我阅读了此，但是当我应用此时，我得到了一个错误float[,] is not compatible with Seq<a'>.但是，此列表也只包含浮点数.

I read this but when I apply this I get an error float[,] is not compatible with Seq<a'>. However this list is also only of floats.

列表功能:

let aggrArraysL data =
    data
    |> Seq.groupBy (fun (a, b, c) -> a)
    |> Seq.map (fun (key, group) ->
        group |> Seq.reduce (fun (a, b, c) (x, y, z) -> a, b + y, (b * c + y * z * 1.)/(b + y)))

数组尝试:

let aggrArrays (data2 : float[,]) =
    data2
    |> Seq.toList
    |> Seq.groupBy (fun (a, b, c) -> a)
    |> Seq.map (fun (key, group) ->
        group |> Seq.reduce (fun (a, b, c) (x, y, z) -> a, b + y, (b * c + y * z * 1.)/(b + y)))
    |> Seq.toArray

我要去哪里错了?谢谢！

Where am I going wrong? thanks!

推荐答案

2D数组实现了IEnumerable，因此您可以使用Seq.cast<T>进行投射:

2D arrays implement IEnumerable so you can just cast them using Seq.cast<T>:

let toList (data2: float[,]) = data2 |> Seq.cast<float> |> Seq.toList

您可能想使其通用:

let toList<'a> (data2: 'a [,]) = data2 |> Seq.cast<'a> |> Seq.toList

看起来您想将数组映射到行元素列表中，而不是将其展平.在这种情况下，您可以执行以下操作:

It looks like you want to map the array into a list of row elements instead of flattening it. In this case you could do:

let aggrArrays (data2:float[,])  =
    [0 .. (Array2D.length1 data2) - 1]
    |> List.map (fun i -> (data2.[i, 0], data2.[i, 1], data2.[i, 2]))
    |> Seq.groupBy id
    |> Seq.map (fun (key, group) -> group |> Seq.reduce (fun (a,b,c) (x, y, z) -> a, b+y , (b*c+y*z*1.)/(b+y)))
    |> Seq.toArray

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