Concatenate a range of Excel cells into a single string specified by a given criteria or condition

ConcatRangeIf.bas

Function ConcatRangeIf(Rc As Range, Criterion As String, Rv As Range, Optional Delimiter As String)
' Concatenate cells into a single string specified by a given criteria or condition

Dim C As Collection: Set C = New Collection     ' Collection of values to be included in final string
Dim Ac() As Variant: Ac = Rc                    ' Criterias
Dim Av() As Variant: Av = Rv                    ' Values
Dim i As Long
Dim j As Long

    For i = LBound(Ac, 1) To UBound(Ac, 1)
        For j = LBound(Ac, 2) To UBound(Ac, 2)
        
            ' Bypass criteria of empty cells if specified
            If Len(Ac(i, j)) > 0 Then
            
                ' Evaluate criteria
                Select Case Left(Criterion, 1)
                    Case ">", "<", "=":
                        If Application.Evaluate(Rc(i, j) & Criterion) Then C.Add Av(i, j)
                    Case Else:
                        If Criterion = Rc(i, j) Then C.Add Av(i, j)
                End Select
                
            End If
            
        Next j
    Next i
    
    ConcatRangeIf = Join(CollectionToArray(C), Delimiter)

End Function

FilterCollection.bas

Private Function FilterCollection(C As Collection, Criterion As String) As Collection
' Filter collection C based on a criterion

Dim NewC As Collection  ' Filtered collection
Dim Ci As Variant       ' Collection element

    For Each Ci In C
    
        ' Evaluate criteria
        Select Case Left(Criterion, 1)
        
            Case ">", "<", "=":
                If Application.Evaluate(Ci & Criterion) Then NewC.Add Ci
                
            Case Else:
                If Criterion = Ci Then C.NewC Ci
                
        End Select
    
    Next Ci
    
End Function