Boolean value does not properly assign based on conditions in for loop - vba

Question

I am quite new to programming and VBA but I have been using a lot of help questions and answers here on stack overflow to learn! I am attempting to create a loop that will determine if a value from a "task" sheet is missing from a "preview" sheet and if so to add the number and line to the "preview" sheet from the "task" sheet. For an example of the data on each sheet:
Task Sheet
TASK VALUE description
11 task 1
12 task 2
13 task 3
Preview Sheet
PREVIEW VALUE Description
1111 preview 1
2222 preview 2
11 task 1
3333 preview 3
13 task 3
The aim is to compare each number in the preview sheet to each value in the task sheet. If a value in the task sheet is not found in the preview sheet, then it should add that value and the entire line into the preview sheet from the task sheet.
My main approach was to create a for loop that would compare each number on the "preview" sheet to each value on the "task" sheet. If it found that two values matched, it would set the variable newTask = False and then exit the nested for loop to move on to the next comparison. If it found that the value from the data sheet was not present in the main sheet, it would set newTask = True and run through until there was no more values to compare. Then, if newTask = True, it would copy and paste the value and line from the data sheet into the main sheet. This is my attempt at coding this:
Dim newTask As Boolean
iP = (Worksheets("parents").Columns("a").Cells.SpecialCells(xlCellTypeConstants).Count) - 1 'count of parent workorders
iC = (Worksheets("child").Columns("a").Cells.SpecialCells(xlCellTypeConstants).Count) - 1 ' count of child workorders
iT = (Worksheets("task").Columns("a").Cells.SpecialCells(xlCellTypeConstants).Count) - 1 ' count of task workorders
iPr = (Worksheets("preview").Columns("a").Cells.SpecialCells(xlCellTypeConstants).Count) + 1 ' this will set iPr one row below the last row on the preview page
nT = 0
Set prRng = Sheets("Preview").Range(Sheets("Preview").Cells(iPr, 1), Sheets("Preview").Cells(iPr, 11))
For n = 1 To iPr
taskWO = Worksheets("task").Cells(n + 1, 1).Value
For nT = 1 To iT
previewWO = Worksheets("preview").Cells(nT + 1, 1).Value
If previewWO = taskWO Then
newTask = False
Exit For
ElseIf previewWO <> taskWO Then
newTask = True
End If
Next nT
If newTask = True Then
Set tRng = Sheets("task").Range(Sheets("task").Cells(n + 1, 1), Sheets("task").Cells(n + 1, 11))
Sheets("Preview").Range(Sheets("Preview").Cells(iPr, 1), Sheets("Preview").Cells(iPr, 11)) = tRng.Value
Sheets("Preview").Cells(iPr, 12) = Sheets("task").Cells(n + 1, 13).Value
iPr = (Worksheets("preview").Columns("a").Cells.SpecialCells(xlCellTypeConstants).Count) + 1
End If
Next n
However, when I run this code, it keeps newTask = True, even if the values do match across the preview and task sheets. Debugging confirmed this and if it comes across similar values, it just continues over it as if they do not equal each other. This causes all values from the task sheet to copy over to the preview sheet, adding many duplicates. I also attempted a Do Until loop but get the same results: Here is my attempt at that:
Dim newTask As Boolean
iP = (Worksheets("parents").Columns("a").Cells.SpecialCells(xlCellTypeConstants).Count) - 1 'count of parent workorders
iC = (Worksheets("child").Columns("a").Cells.SpecialCells(xlCellTypeConstants).Count) - 1 ' count of child workorders
iT = (Worksheets("task").Columns("a").Cells.SpecialCells(xlCellTypeConstants).Count) - 1 ' count of task workorders
iPr = (Worksheets("preview").Columns("a").Cells.SpecialCells(xlCellTypeConstants).Count) + 1 ' this will set iPr one row below the last row on the preview page
nT = 0
taskWO = Worksheets("task").Cells(n + 1, 1).Value
Set prRng = Sheets("Preview").Range(Sheets("Preview").Cells(iPr, 1), Sheets("Preview").Cells(iPr, 11))
For n = 1 To iPr
taskWO = Worksheets("task").Cells(n + 1, 1).Value
Do Until taskWO = previewWO Or nT = iT
previewWO = Worksheets("preview").Cells(nT + 1, 1).Value
nT = nT + 1
If nT = iT Then
Set tRng = Sheets("task").Range(Sheets("task").Cells(n + 1, 1), Sheets("task").Cells(n + 1, 11))
Sheets("Preview").Range(Sheets("Preview").Cells(iPr, 1), Sheets("Preview").Cells(iPr, 11)) = tRng.Value
Sheets("Preview").Cells(iPr, 12) = Sheets("task").Cells(n + 1, 13).Value
iPr = (Worksheets("preview").Columns("a").Cells.SpecialCells(xlCellTypeConstants).Count) + 1
End If
Loop
Next n
I have done a lot of searching but I cannot find any way to get this to stop duplicating values... but I apologize if I missed a thread that has this information or help. I feel like it is something simple but I just cannot figure it out. Could I please get some help on how to correct this? If this is not the correct method, could you also please mention why the loop does not work or what went wrong so I can know in the future? Thank you for any help you provide! If you need some more information, please let me know.

Answer 1

Kyle, without being a complete re-work of your code, here's some code that I think might help you out. If I understand your problem correctly, the main issue you're having is that you're unable to properly determine if a value in one range exists in another. When I have this issue, I usually will use a dictionary object because it's fast, and provides an easy way to check if a value is in a list. To use a dictionary, however, you'll likely have to add a reference to it first. To do this, go to the tools menu and select "References". Scroll down until you've found "Microsoft Scripting Runtime" and select that item. After that, the following code should run just fine.
Sub Testq()
Set Dict = New Dictionary
For Each Cel In Worksheets("preview").Columns(1).SpecialCells(xlCellTypeConstants)
'Add the "Preview Values" of all the cells into your dictionary as Keys.
'Set the value of each key to the "Description" which is in the row next to it.
Dict(Trim(Cel.Value)) = Trim(Cells(Cel.Row(), 2))
Next
'Lets add in the header row of the task worksheet to prevent it from getting coppied over.
Dict(Worksheets("task").Cells(1, 1).Value) = Worksheets("task").Cells(1, 2).Value
'Now loop through all of the values in your "Task" table, checking them against the Dictionary
'to see if there are any new ones.
For Each Cel In Worksheets("Task").Columns(1).SpecialCells(xlCellTypeConstants)
If Not Dict.Exists(Trim(Cel.Value)) Then 'We have a new value.
TaskValue = Trim(Cel.Value)
Description = Trim(Worksheets("Task").Cells(Cel.Row(), 2))
Debug.Print "Yup, I found one that's missing: " & Trim(TaskValue)
'Now add the missing value to the end of your "preview" sheet.
LastRow = Worksheets("preview").Cells(Range("A:A").Rows.Count, "A").End(xlUp).Row
Worksheets("preview").Cells(LastRow + 1, 1) = Trim(TaskValue)
Worksheets("preview").Cells(LastRow + 1, 2) = Trim(Description)
End If
Next
End Sub
Since you mentioned that you're new to VBA, I'll point out that to view the output of the Debug.Print statement, you'll need to display the "Immediate" window. Do this by selecting it from the View menu. As I get a clearer picture of your project, I'll supplement this answer as needed, but for now I hope this will help you solve much of the problem you're having.