Optimize VBA code on lookup without using Vlookup

Source

Target

i have two column in source with 200 rows. In target sheet, have 300 rows. Need to create a lookup from Target to Source to get 2nd column value from Source sheet. I don't want to use VLOOKUP. Currently i am doing thru loop :

 For i =1 to lastrow of Target tab
  for j=1 to lastrow of source tab
   if target.cells(i,1) = source.cells(j,1) then
     target.cells(i,2)= source.cells(j,2)
   exit for
    end if
 next j
next i

This code take too much time as i have 200 columns in source to copy and paste to target tab. Just need any optimization code for the same. Also target tab have more rows compared to source tab data.

A VBA Lookup: Lookup Data Using Worksheet Functions

Sub LookupData()

    ' Workbook
    Dim wb As Workbook: Set wb = ThisWorkbook ' workbook containing this code
    
    ' Source
    Dim sws As Worksheet: Set sws = wb.Sheets("Source")
    Dim slrg As Range: ' lookup
    Set slrg = sws.Range("A2", sws.Cells(sws.Rows.Count, "A").End(xlUp))
    Dim srrg As Range: Set srrg = slrg.EntireRow.Columns("B") ' return
    
    ' Target
    Dim tws As Worksheet: Set tws = wb.Sheets("Target")
    Dim tlrg As Range: ' lookup
    Set tlrg = tws.Range("A2", tws.Cells(tws.Rows.Count, "A").End(xlUp))
    Dim trrg As Range: Set trrg = tlrg.EntireRow.Columns("B") ' return

    ' Lookup
    With Application
        trrg.Value = .IfNa(.Index(srrg, .Match(tlrg, slrg, 0)), "")
        ' in MS365
        'trrg.Value = .XLookup(tlrg, slrg, srrg, "")
    End With

    ' Inform.
    MsgBox "Data looked up.", vbInformation
    
End Sub

A Test

• Your code is slow because you're accessing the cells too many times.
• Here is a sub mimicking your code. Run it to better understand why your code is slow.

Sub LookupDataSlow()
    
    ' Workbook.
    Dim wb As Workbook: Set wb = ThisWorkbook ' workbook containing this code
    
    ' Source
    Dim sws As Worksheet: Set sws = wb.Sheets("Source")
    Dim sLastRow As Long: ' lookup
    sLastRow = sws.Cells(sws.Rows.Count, "A").End(xlUp).Row
    
    ' Target
    Dim tws As Worksheet: Set tws = wb.Sheets("Target")
    Dim tLastRow As Long: ' lookup
    tLastRow = tws.Cells(tws.Rows.Count, "A").End(xlUp).Row

    Dim sRow As Long, tRow As Long
    Dim ReadCount As Long, WriteCount As Long
    
    For tRow = 2 To tLastRow
        For sRow = 2 To sLastRow
            ReadCount = ReadCount + 2
            If sws.Cells(sRow, "A").Value = tws.Cells(tRow, "A").Value Then
                ReadCount = ReadCount + 1
                WriteCount = WriteCount + 1
                tws.Cells(tRow, "B").Value = sws.Cells(sRow, "B").Value
                Exit For
            End If
        Next sRow
    Next tRow
    
    ' Inform.
    MsgBox "Slow Data Lookup" & vbLf & vbLf _
        & "ReadCount: " & ReadCount & vbLf _
        & "WriteCount: " & WriteCount & vbLf _
        & "TotalCount: " & ReadCount + WriteCount, vbInformation
    
End Sub

• On my small data set (see screenshot above), with Exit For, the sheet was accessed 82 times while without it even 116 times. Let us know how many times it was accessed when it ran on your data set.