Prevent Duplicate Data Entry using Cell Validations

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We all know that data validation is a very useful feature in Excel. You can use data validation to create a drop-down list in a cell and limit the values user can enter. But, do you know that you can use data validation in a multitude of ways to prevent users from entering wrong data?

Here is a practical application: Prevent users from entering duplicate values in a range of cells.

For eg. you are making an invoice. Wouldn’t it be cool if Excel prompted you when you enter a duplicate line item so that increase the item quantity instead of repeating it.

Here is a 3 step tutorial to do just that.

Step 1: Identify the range of cells where you want only unique values to be entered

This is simple. All you have to do is find the range where you want to control the user input. Lets say the range is B4:B11

Step 2: Set up Data Validation to prevent duplicate entries

Select the range (B4:B11) and go to data validation (Excel 2007: Data Ribbon > Data Validation, or press ALT+AVV)

Using Data Validation to prevent DuplicatesNow, specify the validation type as “Custom”, this will allow us to use formulas to check for valid data. In our case, we need check if a particular entry is duplicated in the range B4:B11. This can be easily done using COUNTIF formula [learn COUNTIF Formula in plain English].

Go to the formula field and type the countif formula like this: =COUNTIF($B$4:$B$11,B4)<=1

Also, you can set up the “Error Alert” so that you can show a custom message when a duplicate value is typed, like “You have already added that product” message.

Data Validation - Error message

Once you set up error message, it will show up like this:

Data validation to prevent duplicates - error message example
Step 3: Sit back and Relax

The third step is all too familiar. Now that you have prevented duplicate entries in your spreadsheets you can sit back and relax. May be read a few more spreadcheats.

More kickass stuff on data validation (and working with duplicates) using excel

There are a ton of useful articles on the site related to data validation and working with duplicates using excel. Here is a sample. Get started and learn something useful today.

This post is part of our spreadcheats series (yes, the series is still going after one year 😛 )

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26 Responses to “Get busy this weekend, with OR XOR AND [Excel Homework]”

  1. Stef@n says:

    first solution for AND
    The two numbers are in A1 and B1
    = SUBSTITUTE (SUBSTITUTE (A1+B1*9*9, 9, 1), 8, 0)
    regards
    Stef@n

  2. Stef@n says:

    next solution for OR
    =1*SUBSTITUTE (A1+A2;2;1)

    regards
    Stef@n

  3. Stef@n says:

    last solution for XOR
    =1*SUBSTITUTE (A1+A2;2;0)

    regards
    Stef@n

  4. Irvine says:

    Or you could make use of the VBA logical operators!

    Define the following as custom functions
    Public Function BITXOR(x As Long, y As Long)
    BITXOR = x Xor y
    End Function

    Public Function BITAND(x As Long, y As Long)
    BITAND = x And y
    End Function

    Public Function BITOR(x As Long, y As Long)
    BITOR = x Or y
    End Function

    and then use them such:
    A B =BITOR(A,B) =BITAND(A,B) =BITXOR(A,B)
    0101 0100 0101 0100 0001

  5. Stef@n says:

    an another solution for AND
    =1*SUBSTITUTE (SUBSTITUTE (A1+A2;1;0);2;1)

    note:
    the binary numbers are in A1 and A2 !
    regards
    Stef@n

  6. Shair says:

    I was obviously playing hooky at the beach during the bit-wise math lesson – you lost me at “Understanding bit-wise operations” 🙂

  7. Anup Agarwal says:

    After looking at the above solutions, I find my solution silly, but still:

    For the following formulae,
    Row 1: headers,
    Row 2: OR
    Row 3: AND
    Row 4: XOR

    Column 1: Input 1
    Column 2: Input 2
    Column 3: Result

    OR
    {=SUM(IF(MID(A2,ROW(OFFSET($A$1,0,0,LEN(A2),1)),1)+MID(B2,ROW(OFFSET($A$1,0,0,LEN(B2),1)),1)>0,1,0)*10^(LEN(A2)-ROW(OFFSET($A$1,0,0,LEN(B2),1))))}

    AND
    {=SUM(IF(MID(A3,ROW(OFFSET($A$1,0,0,LEN(A3),1)),1)+MID(B3,ROW(OFFSET($A$1,0,0,LEN(B3),1)),1)=2,1,0)*10^(LEN(A3)-ROW(OFFSET($A$1,0,0,LEN(B3),1))))}

    XOR
    {=SUM(IF(MID(A4,ROW(OFFSET($A$1,0,0,LEN(A4),1)),1)+MID(B4,ROW(OFFSET($A$1,0,0,LEN(B4),1)),1)=1,1,0)*10^(LEN(A4)-ROW(OFFSET($A$1,0,0,LEN(B4),1))))}

  8. Hui... says:

    @Anup
    Please don't consider your solution silly
    Firstly, You are the 3rd person to submit an answer
    Secondly, The best formula/function is the one that you know and understand.

  9. Michael Azer says:

    I think I have a very tedious solution, which people won't have the patience to do except in small numbers.

    I used the same problem setup as "Anup Agarwal"

    AND =IF(AND(MID(B2,1,1)="1",MID(C2,1,1)="1"),1,0)&IF(AND(MID(B2,2,1)="1",MID(C2,2,1)="1"),1,0)&IF(AND(MID(B2,3,1)="1",MID(C2,3,1)="1"),1,0)&IF(AND(MID(B2,4,1)="1",MID(C2,4,1)="1"),1,0)

    OR =IF(OR(MID(B3,1,1)="1",MID(C3,1,1)="1"),1,0)&IF(OR(MID(B3,2,1)="1",MID(C3,2,1)="1"),1,0)&IF(OR(MID(B3,3,1)="1",MID(C3,3,1)="1"),1,0)&IF(OR(MID(B3,4,1)="1",MID(C3,4,1)="1"),1,0)

    =IF(OR(AND(MID(B4,1,1)="1",MID(C4,1,1)="0"),AND(MID(B4,1,1)="0",MID(C4,1,1)="1")),1,0)&IF(OR(AND(MID(B4,2,1)="1",MID(C4,2,1)="0"),AND(MID(B4,2,1)="0",MID(C4,2,1)="1")),1,0)&IF(OR(AND(MID(B4,3,1)="1",MID(C4,3,1)="0"),AND(MID(B4,3,1)="0",MID(C4,3,1)="1")),1,0)&IF(OR(AND(MID(B4,4,1)="1",MID(C4,4,1)="0"),AND(MID(B4,4,1)="0",MID(C4,4,1)="1")),1,0)

  10. Michael Azer says:

    Sorry my last post was totally messed up

    AND
    =IF(AND(MID(B2,1,1)="1",MID(C2,1,1)="1"),1,0)&IF(AND(MID(B2,2,1)="1",MID(C2,2,1)="1"),1,0)&IF(AND(MID(B2,3,1)="1",MID(C2,3,1)="1"),1,0)&IF(AND(MID(B2,4,1)="1",MID(C2,4,1)="1"),1,0)
    OR
    =IF(OR(MID(B3,1,1)="1",MID(C3,1,1)="1"),1,0)&IF(OR(MID(B3,2,1)="1",MID(C3,2,1)="1"),1,0)&IF(OR(MID(B3,3,1)="1",MID(C3,3,1)="1"),1,0)&IF(OR(MID(B3,4,1)="1",MID(C3,4,1)="1"),1,0)
    XOR
    =IF(OR(AND(MID(B4,1,1)="1",MID(C4,1,1)="0"),AND(MID(B4,1,1)="0",MID(C4,1,1)="1")),1,0)&IF(OR(AND(MID(B4,2,1)="1",MID(C4,2,1)="0"),AND(MID(B4,2,1)="0",MID(C4,2,1)="1")),1,0)&IF(OR(AND(MID(B4,3,1)="1",MID(C4,3,1)="0"),AND(MID(B4,3,1)="0",MID(C4,3,1)="1")),1,0)&IF(OR(AND(MID(B4,4,1)="1",MID(C4,4,1)="0"),AND(MID(B4,4,1)="0",MID(C4,4,1)="1")),1,0)

  11. Stephen says:

    @stefan,
    I just couldn't get your solutions to work.
    01010101010 + 01010101110 = 02020210120
    what am i doing wrong?

  12. Stephen says:

    @anup
    ...I got yours to work!

  13. Rich says:

    @Stephen - I get the same, but Stef@an's second solution for AND does work (at least for the test cases I used)

  14. Stef@n says:

    @ Stephen / Rich
    yes , you are right ! - only this works:

    OR
    =1*SUBSTITUTE (A1+A2;2;1)
    XOR
    =1*SUBSTITUTE (A1+A2;2;0)
    AND
    =1*SUBSTITUTE (SUBSTITUTE (A1+A2;1;0);2;1)

  15. Michael Azer says:

    @Stef@n - You're answer is really smart, I never knew about the substitute function before. Great Work!

  16. Stef@n says:

    Thx Michael 🙂
    yes - it is simply easy 😉
    if you add 1 and 1 - excel calculate 2
    and then you have to substitute the 2 - new = 0 respectively 1

  17. Rob says:

    Here is a good resource for people wanting to learn binary and hexadecimal.
    http://justwebware.com/bitwise/bitwise.html

  18. Kyle McGhee says:

    Three that weren't asked for:
    NOT
    =SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(A1+A2,0,3),1,0),3,1)

    EQV
    =SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(A1+A2,0,3),2,3),1,0),3,1)

    IMP
    =SUBSTITUTE(SUBSTITUTE(A1+SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(A2,0,3),1,0),3,1),0,1),2,0)

    (was using Daniel Ferry's bitwise file to verify against)

  19. Q says:

    @ Kyle

    Not only takes one parameter and inverts 0 -1 and 1-0

    Took out the +A2
    =SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(A1,0,3),1,0),3,1)

  20. Great solutions!

    I'll add two:

    NAND =1*SUBSTITUTE (A1+A2,2,0)

    NOR=1*SUBSTITUTE(SUBSTITUTE (SUBSTITUTE(A1+A2,0,2),1,0),2,1)

  21. John Fuller says:

    This will work for binary numbers of any size (although the text format mask will have to have as many zeroes as there are digits in the longest addend)

    Assume binary #s are in C35 & C36, then add and format as text in C37:
    =TEXT(C36+C35,"000000000000")
    -sum- = 101112211112

    AND - SUBSTITUTE 0s for 1s in -sum-, then sub 1s for 2s
    =SUBSTITUTE(SUBSTITUTE(C37,"1","0"),"2","1")

    OR - sub 1s for 2s in -sum-
    =SUBSTITUTE(C37,"2","1")

    XOR - sub 0s for 2s in -sum-
    =SUBSTITUTE(C37,"2","0")

  22. Shane says:

    Just wandered by:

    AND:

    =SUBSTITUTE(A1+A2,1,0)/2

  23. Ronald Vonk says:

    Hi Chandoo,

    I am not (yet) really into bitwise calculation, but I am looking for a way to speed up my vba calculation with very big numbers. Would is ben convenient to use bitwise notation for this?

    Best regards,

    Ronald (the Netherlands)
    p.s. love your country!

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