如何在 Mathnet、vb.net 中从矩阵或向量中查找实体索引？

Question

Lets say i have an matrix A=[1 2 3;4 5 6] Now i want to check whether 5 is present in it or not. The answer should be the row and column ie Row=1 Col=1 I have tried find but not finding it useful.

Thanks in advance

Answer 1

With multidimensional arrays we have poor choices. One way is that you loop your array to get element indexes or try something like the code below which loop only your searched number matches.

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

Usage:

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

Answer 2

You can try this

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