如何从 Mathnet、vb.net 中的矩阵或向量中找到实体索引？答案

【问题标题】：How to find entity index from matrix or vector in Mathnet, vb.net?如何从 Mathnet、vb.net 中的矩阵或向量中找到实体索引？
【发布时间】：2020-08-24 08:48:31
【问题描述】：

假设我有一个矩阵 A=[1 2 3;4 5 6] 现在我想检查其中是否存在 5。答案应该是行和列，即行=1 Col=1 我试过 find 但没有发现它有用。

提前致谢

【问题讨论】：

标签： vb.net mathnet-numerics

【解决方案1】：

你可以试试这个

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Dim a As Integer(,) = New Integer(,) {{0, 1, 2}, {3, 4, 5}, {6, 7, 8}, {9, 10, 11}, {12, 13, 14}}

    Dim rw As Integer, cl As Integer

    Dim xy As Integer = 13

    If getXY(a, xy, rw, cl) = True Then
        MessageBox.Show("Row: " & rw & " # Col: " & cl)
    Else
        MessageBox.Show("Not found")
    End If
End Sub

Function getXY(arr As Array, findwhat As Object, ByRef row As Integer, ByRef col As Integer) As Boolean
    Dim d = (From x In arr).ToList.IndexOf(findwhat)
    If d = -1 Then Return False
    row = Math.Ceiling((d + 1) / arr.GetLength(1)) - 1
    col = d Mod arr.GetLength(1)
    Return True
End Function

【讨论】：

【解决方案2】：

对于多维数组，我们的选择很糟糕。一种方法是循环数组以获取元素索引，或尝试类似下面的代码，循环仅匹配您搜索的数字。

ReadOnly matrix(,) As Integer = New Integer(1, 2) {{1, 2, 5}, {4, 5, 6}}

Structure GridData
    Dim Row As Integer
    Dim Col As Integer
End Structure


Function FindIndexesOfNumber(searchedNr As Integer) As List(Of GridData)


    Dim startIndex As Integer = 0
    Dim enumerator As List(Of GridData) = (From elements In matrix).ToList.Where(Function(x) x.Equals(searchedNr)).Select(Function(x)
                                                                                                                              'fake select, it's only for the loop which find numbers  
                                                                                                                              startIndex = Array.IndexOf(matrix.OfType(Of Integer)().ToArray(), searchedNr, startIndex + 1)
                                                                                                                              Dim matrixBound As Integer = matrix.GetUpperBound(1) + 1
                                                                                                                              Return New GridData With {
                                                                                                                               .Col = startIndex Mod matrixBound,
                                                                                                                               .Row = (startIndex \ matrixBound)
                                                                                                                               }
                                                                                                                          End Function).ToList





    For Each c In enumerator
        Console.WriteLine(String.Format("Col: {0} Row: {1}", c.Col.ToString, c.Row.ToString))
    Next

    Return enumerator

End Function

用法：

Dim indexes As List(Of GridData) = FindIndexesOfNumber(5)

【讨论】：