Change color of cells if the value matches values of other worksheets values in a column - excel

Question

So here's the code. I have a calendar with dates in B4:H9. I want to change the color of the cells if the those dates are in a list (column, on different worksheet).
This might be a bit heavy to run if there are many different dates in the worksheet, but that doesn't matter.
What am I doing wrong here? It keeps giving me different error codes, when trying different things.
Sub check_Click()
Dim area As Range
Dim item1 As Range
Dim item2 As Range
Dim sheet As Worksheet
Dim columnlist As Range
sheet = Range("E2").Value
area = Range("B4:H9")
columnlist = Worksheets(sheet).Range("A2:A" & Rows.Count)
For Each item1 In area
For Each item2 In columnlist
If item1.Value = item2.Value Then
item1.Interior.ColorIndex = RGB(255, 255, 0)
End If
Next item2
Next item1
End Sub

Answer 1

As SuperSymmetry mentioned, when you define objects (e.g. ranges, sheets) you need to use the Set keyword. I will not get into that explanation. However few things that I would like to mention...
Try and give meaningful variable names so that you can understand what are they for.
Work with objects so that your code knows which sheet, which range are you referring to.
No need of 2nd loop. Use .Find to search for your data. It will be much faster
To set RGB, you need .Color and not .ColorIndex
Is this what you are trying? (Untested)
Option Explicit
Sub Check_Click()
Dim rngData As Range
Dim rngReference As Range
Dim aCell As Range
Dim matchedCell As Range
Dim ws As Worksheet
Dim lastRow As Long
Dim worksheetName As String
'~~> Change the sheet name accordingly
worksheetName = ThisWorkbook.Sheets("Sheet1").Range("E2").Value
Set ws = ThisWorkbook.Sheets(worksheetName)
With ws
'~~> Find the last row in Col A
lastRow = .Range("A" & .Rows.Count).End(xlUp).Row
'~~> Set your range
Set rngData = .Range("B4:H9")
Set rngReference = .Range("A2:A" & lastRow)
'~~> Loop through your data and use .Find to check if the date is present
For Each aCell In rngData
Set matchedCell = rngReference.Find(What:=aCell.Value, _
LookIn:=xlValues, _
LookAt:=xlWhole, _
SearchOrder:=xlByRows, _
SearchDirection:=xlNext, _
MatchCase:=False, _
SearchFormat:=False)
If Not matchedCell Is Nothing Then
'~~> Color the cell
matchedCell.Interior.Color = RGB(255, 255, 0)
End If
Next aCell
End With
End Sub

Answer 2

This should do the trick, I don't like leaving ranges without their sheet, but since I believe you are using a button, there should be no problem:
Option Explicit
Sub check_Click()
'We are going to use a dictionary, for it to work you need to:
'Go to Tools-References-Check the one called: Microsoft Scripting Runtime
Dim DatesToChange As Dictionary: Set DatesToChange = LoadDates
Dim area As Range: Set area = Range("B4:H9")
Dim item As Range
For Each item In area
If DatesToChange.Exists(item.Value) Then
item.Interior.Color = RGB(255, 255, 0)
End If
Next item
End Sub
Private Function LoadDates() As Dictionary
Set LoadDates = New Dictionary
Dim arr As Variant: arr = ThisWorkbook.Sheets(Range("E2")).Range("A:A")
Dim i As Long
For i = 2 To UBound(arr)
'This here will break the loop when finding an empty cell in column A
If arr(i, 1) = vbNullString Then Exit For
'This will add all your dates in a dictionary (avoiding duplicates)
If Not LoadDates.Exists(arr(i, 1)) Then LoadDates.Add arr(i, 1), 1
Next i
End Function

Answer 3

When you define objects (e.g. ranges, sheets) you need to use the Set keyword
Set area = Range("B4:H9")
Set columnlist = Worksheets(sheet).Range("A2:A" & Rows.Count)
Worksheets() accepts either an Integer or a String. Therefore, sheet should be of Type String
Dim sheet As String
You're also setting columnlist to the whole column in the sheet so you're looping hundreds of thousands more times unncessarily. Change it to
With Worksheets(sheet)
Set columnlist = .Range(.Range("A2"), .Range("A" & Rows.Count).Offset(xlUp))
End With
The above should fix the errors in your code and make it run a little faster. However, there's still big room for improvment in the efficiency of the code. For example, instead of changing the colour inside the loop, you should build a range and set the colour one time after the loop.
Also consider resetting the colour at the beginning of the code with
area.Interior.Pattern = xlNone
I would personally go with conditional formatting as #SiddharthRout suggested in the comments.
Edit following comment
Here's my rendition
Sub check_Click()
Dim dStart As Double
dStart = Timer
Dim rngCalendar As Range
Dim vCalendar As Variant
Dim shtDates As Worksheet
Dim vDates As Variant, v As Variant
Dim i As Long, j As Long
Dim rngToColour As Range
' Change the sheet name
With ThisWorkbook.Sheets("Calendar")
Set rngCalendar = .Range("B4:H9")
vCalendar = rngCalendar.Value
Set shtDates = ThisWorkbook.Sheets(.Range("E2").Value)
End With
With shtDates
vDates = .Range(.Range("A2"), .Range("A" & Rows.Count).End(xlUp)).Value
End With
For i = 1 To UBound(vCalendar, 1)
For j = 1 To UBound(vCalendar, 2)
For Each v In vDates
If v <> vbNullString And v = vCalendar(i, j) Then
If rngToColour Is Nothing Then
Set rngToColour = rngCalendar.Cells(i, j)
Else
Set rngToColour = Union(rngToColour, rngCalendar.Cells(i, j))
End If
Exit For
End If
Next v
Next j
Next i
rngCalendar.Interior.Pattern = xlNone
If Not rngToColour Is Nothing Then
rngToColour.Interior.Color = RGB(255, 255, 0)
End If
MsgBox "Time taken: " & Format(Timer - dStart, "0.0000s")
End Sub
With a list of 2500 dates it took 0.0742s on my machine.