Faster way of using Sumifs()

Here’s another way:

EDIT – updated to add “averageifs” and “sumifs” to my initial (mistaken) “countifs” version…

Sub SetupDummyData()
    Const NUM As Long = 100001
    Range("A1:E1").Value = Array("A_Header", "B_Header", "C_Header", "Value", "ResultHere")
    Range("A2:A" & NUM).Formula = "=""A#"" & round(RAND()*10,0)"
    Range("B2:B" & NUM).Formula = "=""B#"" & round(RAND()*10,0)"
    Range("C2:C" & NUM).Formula = "=""C#"" & round(RAND()*10,0)"
    Range("D2:D" & NUM).Formula = "=round(RAND()*100,1)"
    
    Range("A2:D" & NUM).Value = Range("A2:D" & NUM).Value
End Sub


Sub Tester()
    
    Dim arr, ws, rng As Range, keyCols, valueCol As Long, destCol As Long, i As Long, frm As String, sep As String
    Dim t, dict, arrOut(), arrValues(), v, tmp, n As Long
    
    keyCols = Array(1, 2, 3)  'these columns form the composite key
    valueCol = 4              'column with values (for sum)
    destCol = 5               'destination for calculated values
    
    t = Timer
    
    Set ws = ActiveSheet
    Set rng = ws.Range("A1").CurrentRegion
    n = rng.Rows.Count - 1
    Set rng = rng.Offset(1, 0).Resize(n) 'exclude headers
    
    'build the formula to create the row "key"
    For i = 0 To UBound(keyCols)
        frm = frm & sep & rng.Columns(keyCols(i)).Address
        sep = "&""|""&"
    Next i
    arr = ws.Evaluate(frm)  'get an array of composite keys by evaluating the formula
    arrValues = rng.Columns(valueCol).Value  'values to be summed
    ReDim arrOut(1 To n, 1 To 1)             'this is for the results
    
    Set dict = CreateObject("scripting.dictionary")
    'first loop over the array counts the keys
    For i = 1 To n
        v = arr(i, 1)
        If Not dict.exists(v) Then dict(v) = Array(0, 0) 'count, sum
        tmp = dict(v) 'can't modify an array stored in a dictionary - pull it out first
        tmp(0) = tmp(0) + 1                 'increment count
        tmp(1) = tmp(1) + arrValues(i, 1)   'increment sum
        dict(v) = tmp                       'return the modified array
    Next i
    
    'second loop populates the output array from the dictionary
    For i = 1 To n
        arrOut(i, 1) = dict(arr(i, 1))(1)                       'sumifs
        'arrOut(i, 1) = dict(arr(i, 1))(0)                      'countifs
        'arrOut(i, 1) = dict(arr(i, 1))(1) / dict(arr(i, 1))(0) 'averageifs
    Next i
    'populate the results
    rng.Columns(destCol).Value = arrOut
    
    Debug.Print "Checked " & n & " rows in " & Timer - t & " secs"

End Sub