VBA Filter Column Store Unique Values of Another Column

I'm trying to accomplish the following.

1. Filter Column A
2. Grab Unique values from Column B

So given the following table...

I'd like to filter for "One" in column A and get an array back that I can paste unto column C like this...

I've tried to use dictionaries but I have little understanding of how that works. There can be thousands of rows so speed can be an issue and I'd rather not loop through each if it's not necessary.

I've seen solutions that bring back unique values of a column using advanced filter but never a combination of filtering one column and then using the filtered results to get a unique list of values.

Example of code (partial) I've tried:

On Error Resume Next
    enterpriseReportSht.ShowAllData
On Error GoTo 0
With enterpriseReportSht
    .AutoFilterMode = False
    With .Range(Cells(1, 1).Address, Cells(entRptLR, entRptLC).Address)
        .AutoFilter Field:=manLevel2CN, Criteria1:=userInputsArr(i, manLevel2InputCN)
        '.SpecialCells(xlCellTypeVisible).Copy Destination:=resultsSht.Range("A1")
    End With
End With
filteredColArr = enterpriseReportSht.UsedRange.columns(manLevel4CN).Value
RemoveDuplicatesFromArray (filteredColArr)

with this function:

Public Function RemoveDuplicatesFromArray(sourceArray As Variant)
Dim duplicateFound As Boolean
Dim arrayIndex As Integer, i As Integer, j As Integer
Dim deduplicatedArray() As Variant

arrayIndex = -1
deduplicatedArray = Array(1)

For i = LBound(sourceArray) To UBound(sourceArray)
    duplicateFound = False

    For j = LBound(deduplicatedArray) To UBound(deduplicatedArray)
        If sourceArray(i) = deduplicatedArray(j) Then
            duplicateFound = True
            Exit For
        End If
    Next j

    If duplicateFound = False Then
        arrayIndex = arrayIndex + 1
        ReDim Preserve deduplicatedArray(arrayIndex)
        deduplicatedArray(arrayIndex) = sourceArray(i)
    End If
Next i

RemoveDuplicatesFromArray = deduplicatedArray
End Function

My concerns with it is that it's not grabbing the filtered data. It's grabbing all of it I believe. I'm also getting an error with the remove duplicates function.

This should do what you are looking for using a dictionary.

You could speed it up by loading the range into an array and iterating through that, but it's a bit of a pain to do that with a filtered range as well as getting the upperbound of a two dimensional array, you'll need to transpose it into a one dimensional array first. Probably not worth it unless you notice the speed is really slow. I tested with 15k rows it was < 1 second.

    Dim i As Long
    Dim lr As Long
    Dim filterrange As Range
    
    Dim dict As Object
    Set dict = CreateObject("Scripting.Dictionary")
    
    
    With Sheet1 'Change as needed
        lr = .Cells(.Rows.Count, 1).End(xlUp).Row
        Set filterrange = .Range(.Cells(1, 1), .Cells(lr, 2))
        filterrange.AutoFilter 1, "One"
        
        lr = .Cells(.Rows.Count, 1).End(xlUp).Row 'Only really necessary if you have a lot of rows
        
        For i = 1 To lr
            If .Rows(i).EntireRow.Hidden = False Then
                If Not dict.exists(.Cells(i, 2).Value) Then
                    dict.Add .Cells(i, 2).Value, ""
                End If
            End If
        Next i
        filterrange.AutoFilter
        
        Dim key As Variant
        i = 1
        For Each key In dict
            .Cells(i, 3).Value = key
            i = i + 1
        Next key
    End With