Question

I need to merge cells using a formula so that the cells only merge when cells on another tab are filled.
I have 2 tabs with the same amount of columns in each. I want cells a1-d1 to merge in tab 1 when cells a1-d1 in tab 2 are filled and for the value of d1 in tab 2 to be inputted into the newly merged cells in tab 1.
this is what I have:

Answer 1

Excel VBA Methods and Function (Excel Macros) overview

Since you want to change cells i do not believe that you can use a formula (even not a user defined one). Therefore i wrote an excel vba macro for your problem.

• FirstRows(): Is the starting point. It loops over 10 rows and calls the other methods
• CheckEmptyCellValues(curRow): This method checks for empty cells in tab2 (sheet 2 in excel)
• MergeCells(curRow) takes the current row as a number (any integer from 1 to max amount of rows) and merges the cells from column 1 to 4 on Sheet 1 (the first sheet in excel)

Fully working demo tested with 4 columns and 10 rows

Sub FirstRows()
   Sheets(1).Select
   For curRow = 2 To 11
      Merge = CheckEmptyCellValues(curRow)
      If Merge = 4 Then
        MergeCells (curRow)
        cellValue = Sheets(2).Cells(curRow, 4).Value
        Sheets(1).Cells(curRow, 1).Value = cellValue
      End If
   Next
 End Sub
  
Sub MergeCells(curRow)
    Sheets(1).Select
    Range(Cells(curRow, 1), Cells(curRow, 4)).MergeCells = True
End Sub

Function CheckEmptyCellValues(curRow)
    Merge = 0
    Sheets(2).Select
    For i = 1 To 4
        If Len(Cells(curRow, i).Value) > 0 Then
            Merge = Merge + 1
        End If
    Next
    CheckEmptyCellValues = Merge
End Function

Below you can see the result. The values from sheet 2 haven been copied to sheet 1 (second image). In Sheet 1 the Cells in a row are merged (in row 2 from Cell A2 up to Cell D2 (A2-D2 is now just one cell) if in the first image (sheet 2) every cell (from column a to column d) in a row had a value.

Bugs in the modified code

There are a few things in the modifiend code that are not possible or could lead to a wrong understanding

Function CheckEmptyCellValues(curColumn) 
  Merge = 0 
  Sheets(2).Select 
  For i = A To d 
    If Len(Cells(curColumn, 11).Value) > 0 Then 
        Merge = Merge + 1 
    End If 
  Next 
  CheckEmptyCellValues = Merge 
End Function

1. The line For i = A To d is not possible. If you want to use a loop you have to use numbers: For i = 1 To 4 this would repeat the code between For and Next4 times starting with 1
2. This line Cells(curColumn, 11).Value is technical correct but misleading. Excel uses the first value after (for the row-index and the second value for the column-index. Both values have to be a number: Cells(4,2).Value returns the Cell value from the 4th. row and the second Column (in the Excel Gui the Cell B4)

Try changing this line For i = A To d to this For i = 1 To 4 and see if that returns the wished result.

Bugs part 2

In your other modification you have some of the same bugs:

• The loop For curColumn = A to d needs numbers instead of letters (unless A and d were a variable filled with a number but according to your code sample this is not the case
• The line cellValue = Sheets(2).Cells(curColumn, d).Value has the same bug, if d is just the letter d and not something like d = 4 than you can not use it in a loop.

This is the code from your comment:

 Sub FirstRows() 
  Sheets(1).Select 
    For curColumn = A To d 
       Merge = CheckEmptyCellValues(curColumn) 
       If Merge = d Then 
          MergeCells(curColumn) 
          cellValue = Sheets(2).Cells(curColumn, d).Value 
          Sheets(1).Cells(curColumn, d).Value = cellValue 
       End If
    Next 
  End 
  Sub Sub MergeCells(curColumn) 
     Sheets(1).Select 
     Range(Cells(curColumn, 1), Cells(curColumn, d)).MergeCells = True 
  End Sub

Be carefull it is not running.