Paste from list not found in current range to bottom of current range - excel

Question

I have column A that has all existing categories, new categories are listed in column C. I'm trying to determine how to take these new categories, and add them to column "a" if they aren't already in column A. In the example the new categories in column C are added to column A even if there are already in column A. I would also need range("a1") in the if-then line to be a dynamic range since new categories will be added as the code runs. Some constructive criticism would be greatly appreciated as well to help me in the future.
Sub newcategory()
Dim newcatcount As Integer
Dim i As Integer
newcat = Range("c100000").End(xlUp).Row
For i = 1 To newcat
If Cells(i, 3).Value <> Range("a1") Then
Cells(i, 3).Select
Selection.copy
Range("a100000").End(xlUp).Offset(1, 0).Select
ActiveSheet.Paste
End If
Next
End Sub

Answer 1

Please give this a try...
Sub AddNewCategories()
Dim lrA As Long, lrC As Long, i As Long, j As Long
Dim x, y, z(), dict
lrA = Cells(Rows.Count, 1).End(xlUp).Row
lrC = Cells(Rows.Count, 3).End(xlUp).Row
'Array to hold the categories in column A starting from Row1, assuming the categories start from A1. If not, change it accordingly.
x = Range("A1:A" & lrA).Value
'Array to hold the new categories in column C starting from Row1, assuming the categories start from C1. If not, change it accordingly.
y = Range("C1:C" & lrC).Value
Set dict = CreateObject("Scripting.Dictionary")
For i = 1 To UBound(x, 1)
dict.Item(x(i, 1)) = ""
Next i
For i = 1 To UBound(y, 1)
If Not dict.exists(y(i, 1)) Then
dict.Item(y(i, 1)) = ""
j = j + 1
ReDim Preserve z(1 To j)
z(j) = y(i, 1)
End If
Next i
If j > 0 Then
Range("A" & lrA + 1).Resize(j).Value = Application.Transpose(z)
End If
Set dict = Nothing
End Sub

Answer 2

you could use excel built in RemoveDuplicates() function, as follows (mind the comments):
Option Explicit
Sub newcategory()
Dim newcat As Range
With Worksheets("Categories") ' change "Categories" to your actual sheeet name
Set newcat = .Range("C1", .Cells(.Rows.Count, 3).End(xlUp)) ' get the range of all nwe categories in reference sheet column C from row 1 down to last not empty one
.Cells(.Rows.Count, 1).End(xlUp).Resize(newcat.Rows.Count).Value = newcat.Value ' append new categories values below existing categories in column A
.Range("A1", .Cells(.Rows.Count, 1).End(xlUp)).RemoveDuplicates Columns:=Array(1), Header:=xlNo ' remove duplicates
End With
End Sub